Agavaceae

S. Verhoek

Agavaceae Endl, Enchiridion: 105 (1841), nom. cons.

Plants small to gigantic, perennial, monocarpic or polycarpic, acaulescent or arborescent, sometimes caespitose. Roots fibrous or fleshy; rhizomes spreading or thick and upright. Leaves rosulate, spiral, annual or long-lived, linear, lanceolate, elliptic or ovate, fibrous, rigid or flexible, the texture thin, thickened and hard, or succulent, pale to dark green, often glaucous, maculate in some species; the apex with a short or long soft or pungent point; margins entire, denticulate to coarsely toothed or filiferous. Flowering stems terminal or axillary, sometimes huge, bracteate. Inflorescence a panicle, raceme, or spike. Flowers perfect, often protandrous, hypogynous, or epigynous, actino-morphic to zygomorphic, never provided with a pericladium or articulate with the pedicel. Tepals 6, petaline, semisucculent, waxy, green, greenish yellow or white, sometimes tinged with maroon, or red to coral, free or united into a long or short tube, the lobes erect, spreading or revolute. Stamens 6, with long or short filaments, included or long exserted; filaments thin or variously thickened, smooth, papillate or short-hairy, the long ones bent in bud; anthers bithecate, dorsifixed, versatile, linear, oblong, or sagittate, introrsely dehiscent with longitudinal slits. Gynoecium of 3 united carpels, ovary superior or inferior, trilocular, ovoid to cylindrical, fleshy, with septal nectaries; ovules numerous, in 2 axile rows in each locule, anatropous; style single or styluli free (Yucca), long or short, included or exserted, thickened in Furcraea, Beschomeria, and Yucca; stigma single and capitate or 3-lobed or (Yucca) stigmas 3 on separate branches. Fruit a loculicidally dehiscent, erect capsule, or (Yucceae) sometimes septicidally dehiscent, or indehiscent and dry or fleshy. Seeds mostly flat, sometimes bordered with a narrow wing, cuneate, black. Embryo cylindrical, straight or slightly curved, oriented along the long axis of the seed.

The family as presently circumscribed is entirely New World temperate and tropical, with 8 genera and ca. 300 species.

Vegetative Morphology. The large members of the family such as Furcraea and some Agave can be massive rosettes up to 4 m broad with xeromorphic leaves persistent for 8-15 years. Some species of Yucca attain treelike form. Genera with primarily smaller members such as Manfreda and Polianthes have softer leaves and occupy dry to mesic habitats. In Agave, horizontal anchoring roots spread to a considerable distance. Certain species in most genera produce horizontal rhizomes, and in Manfreda, Polianthes, and Prochnyanthes (Verhoek-Williams 1975) and in Yucca elata (J. Webber 1953) there is an upright globose to cylindrical tuberlike rhizome.

Stems vary from very short to treelike and may be branched. Branching in Yucca is sympodial. There is secondary thickening growth in stems of at least Agave, Furcraea, and Yucca. The leaves are arranged in spirals at the top of the stems, giving rise to the rosette form in short species or to a palmlike tree habit. Yucca approaches a 2/5 phyl-lotaxy (Arnott 1962).

Leaves throughout the family may be deeply channeled. The leaves in Manfreda, Polianthes, and Prochnyanthes are thin to only slightly succulent, but in Yucca, and especially Agave and Furcraea, they are thickened over their whole width and thickest at the center. Leaf tips are diagnostic. Those of Agave, Hesperaloe, and Yucca are a hard pungent spine, those of Furcraea a hard button or short point, and those of Beschorneria, Manfreda, Polianthes, and Prochnyanthes are soft points. Leaf margins may be entire or with small translucent teeth. Additionally, in Furcraea and Agave the margins may be provided with large corneous teeth which may be diagnostic for species. Filiferous margins occur in Agave, Hesperaloe, and Yucca.

Vegetative Anatomy. The roots contain vessels with simple and scalariform perforation plates (Wagner 1977). Vessels are absent in stems and leaves. The fleshy roots in the family have a large cortical parenchyma. A multilayered velamen is reported in Agave (v. Guttenberg 1968) and a thick endodermis in Yucca (Arnott 1962). The primary root in Agave is tetrarch (Boyd 1932). Primary and adventitious roots in Yucca have 4 to 28 protoxylem poles, depending upon the species.

Leaves in both Yucca and Agave contain bundles of acicular crystals of calcium oxalate. In Yucca brevifolia these crystals are 4-sided raphides, while in Agave americana there are 6-sided raphides with laminated sheaths, and styloids cov ered with suberinic sheaths (Wattendorf 1976). Cells walls of the cells containing styloids are also suberized. Sieve-tube plastids have cuneate protein crystals only (Behnke 1981).

Based upon stomatal complexity and leaf epidermal characteristics, the genera fall into two broad ecologically adapted groups (Alvarez 1990). These groups mainly follow generic lines, but particular species may align with the other group. Those genera with persistent leaves adapted to dry conditions (Agave, Beschorneria, Furcraea, and Yucca) have a thick cuticle, isodiametric epidermal cells and projections from the subsidiary cells which make complex chambers around the stomata (Blunden and Binns 1970; Blunden et al. 1973; Alvarez 1990). Prochnyanthes also falls in this group. In the "herbaceous" genera Manfreda and Polianthes, the epidermal cells are tabular and the stomata are without complex stomatal chambers. Papillate epidermal cells are arranged over veins in Prochnyanthes, Hesperaloe, and Yucca section Hesperoyucca. Groups of nonuniform papillate cells form ridges in Yucca, Furcraea, and Beschorneria. Rows of papillae are also present in Manfreda. Pubescence is not common in the family, but where it occurs, trichomes are simple. These characters, along with those of stomata, may be diagnostic at the species level and at the section level in Agave (Gentry and Sauck 1978).

Stomata are largely anomocytic in Polianthes tuberosa (Shah and Gopal 1970) but paracytic, tricytic, and tetracytic types also occur. Stomata are paracytic in Manfreda, Polianthes, and Prochnyanthes and tetracytic in Agave, Beschorneria, Furcraea, and many Yucca (Blunden et al. 1973; Gentry and Sauck 1978) and also anomocytic in Yucca (Blunden and Binns 1970). The stomata are sunken below the epidermal cells because the subsidiary cells are dilated above and below the guard cells. The suprastomatal chamber is guarded and sometimes compartmentalized by 6 lips in Yucca and 4-15 lips in Agave, Beschorneria, and Furcraea. Hosta, previously included in the family, has very different and specialized epidermal and stomatal characters. Leucocrinum and Hesperocallis, also thought to be allied to the family, are anomocytic and less specialized.

In the leaves, palisade tissue may or may not be differentiated and the mesophyll may be largely composed of groups of water-storage cells (Blunden et al. 1973).

Secondary growth in stems of Yucca and Agave results in alternating dense and parenchymatous rings (Arber 1925). In Yucca whipplei the primary and secondary thickening meristems are longitu dinally continuous and occur functionally and histologically as phases in the activity of the same meristem (Diggle and DeMason 1983). The bark in arborescent yuccas is thick.

In the leaves, vascular and fiber bundles occur in arcs in regular or irregular rows adjacent to the epidermis or palisade layers and through the center of the leaf. Bundles of heavily lignified mechanical fibers occur mainly at the periphery of the leaf. Fibers may occur at both phloem and xylem poles of vascular bundles. The presence and degree of development in these fiber caps and the arrangement of fiber bundles is diagnostic for Agave, Beschorneria, and Furcraea (Blunden et al. 1973). A bundle sheath of longitudinally elongated parenchyma cells is present in Agave and Yucca but absent in Beschorneria and Furcraea. Gross fiber characters in Agave have been analyzed for the fiber industry (Lock 1969). Individual leaf fiber cells in species of Hesperaloe and Yucca are longer (>2mm) and narrower (<20¡am) than those of Agave sisalana (McLaughlin and Schuck 1991). In species with filiferous leaf margins the margin is set off from the main part of the leaf by layers of lignified cells and abscission cells.

Inflorescence Structure. Inflorescences in the family vary from paniculate to racemose or spicate. Except in some species of Yucca, the flowering portion is commonly borne on a tall, bracte-ate peduncle (Fig. 24). Among those with a spicate or racemose inflorescence, flowers in Manfreda are solitary at the nodes, in Polianthes and Prochnyanthes the flowers are paired, and in Agave subgen. Littaea the flowers are commonly clustered at each node.

The panicles of Agave subgen. Agave (Fig. 25) bear the flowers clustered in smaller umbellate panicles at the ends of secondary and tertiary branches (Catalano 1931) and in some species may reach heights of 8-12m. In Beschorneria, Furcraea, Hesperaloe, and Yucca the inflorescence is a raceme or panicle, often within the same species. The panicles are evenly floriferous with individual flowers or clusters of up to 10 flowers spread at regular intervals along the branches. Normally paniculate agaves and yuccas may become spicate by contraction of lateral branches (McKelvey 1947; Gentry 1982).

In Polianthes and Prochnyanthes each pair of flowers occurs in the axil of a single bract and each flower is subtended by a bract. In Manfreda there is 1, occasionally at the lower nodes 2, flowers in the axil of each bract, each pedicel having 2 lateral bracteoles (Verhoek-Williams 1975).

Manfreda Longibracteata

Fig. 24A-K. Agavaceae. A-F Hesperaloe parviflora. A Habit. B Leaf. C Flower. D, E Stamen. F Pistil. G, H Manfreda longibracteata. G Flower. H Bulbous rhizome. I, J Prochnyanthes mexicana. I Habit. J Opened flower. K Polianthes durangensis, flower. (A-F, I-K Takhtajan 1982)

In Agave and Furcraea the inflorescence occasionally produces plantlets.

Flower Structure. Yucca and Hesperaloe have superior ovaries and Agave, Manfreda, Polianthes, Prochnyanthes, Furcraea, and Beschorneria have inferior ovaries. Intermediates between these two conditions occur. In Hesperaloe nocturna the basal part of the ovary is surrounded by

Polianthes Durangensis
Fig. 25A-C. Agavaceae. Agave cerulata subsp. cerulata. A Partial inflorescence. b Flower, longitudinal section. C Opening fruit. (Takhtajan 1982)

receptacular tissue. The tip of the ovary in Agave striata, Manfreda guttata, and several other species protrudes into the floral tube (Verhoek-Williams 1975).

The tepals are united into a tube in Agave, Manfreda, Polianthes, and Prochnyanthes, are free or nearly so in Yucca and Furcraea and some Hesperaloe, or so closely appressed as to approximate a tube in Beschomeria and some Hesperaloe. Flowers with short tubes or none are actino-morphic. Long-tubed flowers of Polianthes and Manfreda, and flowers of Agave section Parviflorae are frequently zygomorphic: the tubes are curved, the mouth of the flower is overarching at the top, and the stamens (and later the style) are held along the top of the tube.

The stamens are inserted either at the tepal base, at characteristic levels in the tube, or sometimes at different levels (Manfreda potosina and Agave sect. Ditepalae). Filaments in Agave, Polianthes, and Manfreda are usually long and slender, included or exserted and then initially bent in bud, but in some species of Polianthes and Manfreda the filaments are short and inserted at the mouth of the tube. The filaments in Furcraea are swollen in the basal portion and abruptly narrowed distally. In Yucca the filaments are sometimes pu-berulent, and the tips frequently swollen and turned outward. Anthers are oblong to linear except in Yucca and Hesperaloe, where they are sagittate to hastate.

In the ovaries, septal nectaries have been reported in Agave, Beschomeria, Furcraea, Polianthes, and Yucca. In Yucca, Furcraea, and Beschomeria the nectaries are augmented with external secretory grooves along the ovarian septa (Arber 1925). Nectar amounts in Yucca are small, copious in Agave (Schaffer and Schaffer 1977) and Manfreda scabra (Eguiarte and Burquez 1987).

The style is elongate except in some species of Yucca. In Beschomeria, and more so in Furcraea, it is swollen into 3 basal ridges and abruptly narrowed distally. At anthesis the long style of Agave, Polianthes, Manfreda, and Prochnyanthes is not yet fully extended and may be bent downwards out of the circle of stamens. The broad style of Yucca is often short and not clearly demarcated from the ovary.

Stigmas in the family are 3 or there is a single 3-lobed or capitately 3-angled stigma. In Polianthes and a few species of Manfreda the stigma lobes reflex at maturity. Most Yucca species have 3 stigmas but Yucca sect. Hesperoyucca has a capitate 3-lobed stigma. The stigmas in Agave, Furcraea, and Yucca are of the Dry type with unicellular papillae and those of Beschomeria and some species of Agave are of the Wet type with low to medium papillae (Heslop-Harrison and Shivanna 1977). Polianthes and Manfreda have stigmas that are moist when receptive.

Floral Anatomy. Floral anatomy has been described in detail for Agave lechuguilla (Grove 1941) and Polianthes tuberosa (Joshi and Pantulu 1941). The floral parts arise acropetally. The stamens arise in 2 cycles of 3 but mature simultaneously. Vascular anatomy of the flower is simple. Bundles are present at the base of the ovary and continue with minimum divergence into the separate floral parts.

Embryology. In Agave the middle layer of the anther wall has 10-12 layers and the endothecium is multilayered with fibrous thickenings (Davis 1966). There is a 2-layered endothecium in Polianthes. In the family, tapetal cells are 2-4-nucleate. Microsporogenesis is successive and the pollen grains are 2-celled at anthesis.

The ovules are anatropous, bitegmic, and crassinucellate. In Yucca the nucellus divides and becomes a perisperm (Arnott 1962). The hypodermal archesporial cell cuts off a parietal cell, which divides to form 2 or 4 cells (Wolf 1940; Joshi and Pantalu 1941) or a single parietal layer (Grove 1941). The megaspore tetrad is linear (Mogensen 1970) or T-shaped. The chalazal megaspore di-

vides to produce a normal Polygonum type embryo sac in Yucca, Agave, Manfreda, and Polianthes. In Furcraea the micropylar megaspore is the functional one. The polar nuclei fuse before fertilization. The mature embryo sac is narrowed toward the chalaza and the narrowed portion is interpreted as having a haustorial function (Wolf 1940). Endosperm formation is Helobial in Yucca, Agave, and Beschorneria, and nuclear in Furcraea (Joshi and Pantulu 1941).

Pollen Morphology. Pollen studies of 15 genera historically included in the family show 7 types based upon aperture and exine ornamentation, and help to support a narrow circumscription of the family (Ojeda and Ludlow-Wiechers 1995; see also Alvarez and Köhler 1987). Semitectate, primarily sulcate grains occur in Agave, Beschorneria, Dasylirion, Hesperaloe, Manfreda (Fig. 26A), and Polianthes. Exine ornamentation in Furcraea is tectate perforate to semitectate. Yucca has tectate perforate, sulcate grains. Tetrads occur simultaneously with monads in Beschorneria and Furcraea (Fig. 26B). Bisulcate grains have been reported in Polianthes and Prochnyanthes (Erdtman 1969). The pollen grains are prolate or subprolate and the sulcus is nearly as long as the axis of the grain.

Karyology. The base number of the family is x = 30, with a karyotype of 5 long and 25 short chromosomes (Granick 1944; Gomez-Pompa et al. 1971). This complement is a major distinguishing characteristic of the family as presently circumscribed. Only Hosta (Funkiaceae) and Hesperocallis have similar bimodal karyotypes. Half of the species of Agave counted are polyploid, most of these in subgen. Agave. Tetraploids are also reported for Polianthes tuberosa.

Pollination and Reproductive Systems. Floral traits of color, odor, shape, nectar production, and timing of anthesis attract specific moth, hummingbird, and bat pollinators. Yucca spp. are pollinated by females of the yucca moth Tegiticula which collect pollen and pack it into stigmas of ovaries in which they oviposit (Powell and Mackie 1966; Dodd and Linhart 1994). Two species are pollinated by moth species unique to them, Y. whipplei by T. maculata (Riley) and Y. brevifolia by T. paradoxa (Riley). All other Yucca spp. are pollinated by T. (=Pronuba) yuccasella (Riley) (McKelvey 1947). There is either early abortion of infested fruits or later seed predation by the yucca moth larvae (Richter and Weis 1995). When moth

Pollen Yucca Elephantipes
Fig. 26A,B. Agavaceae. A Manfreda variegata, distal face of pollen grain showing sulcus with narrow and compact margin, SEM X1000. B Furcraea macrophylla, pollen tetrad. SEM X900. (Photo Alvarez and Koehler)

populations are low, the fly Pseudocalliope may be an important alternate pollinator (Dodd and Linhart 1994).

Flowering and pollination have been investigated in Agave by Schaffer and Schaffer (1977) and Howell (1979); in Hesperaloe by Starr (1995); and in Manfreda, Polianthes, and Prochnyanthes by Verhoek-Williams (1975), Verhoek (1978a), and Eguiarte and Burquez (1987). Most species of Agave and Polianthes are protandrous by several days. Anther dehiscence and nectar production occur at particular times of the day. Both nocturnal and diurnal flowering occur in Agave. Prochnyanthes and Manfreda are nocturnal. Hesperaloe and Polianthes have whitish, fragrant, nocturnal flowers or diurnal and crepuscular red flowers. Nocturnal odors in white-flowered Polianthes and some greenish Manfreda are floral and fruity; other greenish Manfreda flowers produce alliaceous odors.

Some species of Agave, mainly of subgen. Agave, are adapted to pollination by bats, other species by bumblebees and carpenter bees. Hummingbird and hawkmoth pollination is recorded in Manfreda, Prochnyanthes, Polianthes, and Hesperaloe. Bat pollination is also recorded for Manfreda scabra and Hesperaloe.

Protandry in the family may encourage cross-pollination but the amount may be low. Flowers bloom in succession at a node or up the spike so that male and female phase flowers are present in the inflorescence at the same time. Self-compatibility has been demonstrated in many of the genera.

Self-compatibility has been demonstrated in Manfreda and Polianthes (Verhoek-Williams 1975), in Yucca (Dodd and Linhart 1994; Richter and Weis 1995), and reported for Agave (Gentry 1982). However, seed set is lower by about 20% in self-pollinated Manfreda scabra (Eguiarte and Biirquez 1987). Howell and Roth (1981) have shown in A. palmeri that self-pollination does not usually result in fruit set.

Artificial interspecific crosses have been made in Hesperaloe (Starr 1995), Polianthes (Bundrant 1985), and Manfreda and between Manfreda and Polianthes (Verhoek-Williams 1976). Hybrids are postulated in Agave (Gentry 1982) and Yucca (J. Webber 1953).

Fruit and Seed. Most genera have loculicidal capsules except in several sections of Yucca, where the fruits may be indehiscent, and then they are dry and spongy in sect. Clistocarpa, and pendent, fleshy ("baccate"), and sweet with a hard endocarp in sect. Sarcocarpa. Capsule dehiscence in Yucca sect. Chaenocarpa is septicidal and also apically loculicidal.

The seeds are usually numerous in a capsule. They are 2-17mm long, flat, black, and asymmetrically cuneate and sometimes narrowly winged. In the outer cell layer of the outer integument there is always a brittle phytomelan crust present; in Yucceae it is 10-40 (im thick, in the Agaveae ca. 10 ^m. The epidermal cells of Y. whipplei seed coats contain raphides. The inner integument collapses and loses its cellular structure (Huber 1969).

Storage tissue in the seed of Yucca is reported as perisperm (Arnott 1962), and as endosperm in the other genera. Seeds contain lipids and proteins, and some seeds have large amounts of saponins.

The embryo is linear, cylindrical, straight, or slightly curved, extending generally along the greatest length of the seed from the chalazal end. Seeds of species of Yucca with baccate fruits are ruminate.

Seedlings are similar in at least 5 of the genera (Boyd 1932; Arnott 1962), with the cotyledon photosynthetic.

Dispersal and Reproductive Biology. Members of the Agavaceae are efficient vegetatively propagating plants. All genera produce new plants by lateral budding from the parent plant, either directly or from the tips of spreading rhizomes. In Furcraea and some species of Agave, multiple plantlets are produced in the inflorescence. As a result, a whole population may consist of only 1 or several clones. Commercial agaves, such as A. sisalana and A. tequilana, are propagated by vegetative offshoots.

Seed dispersal in the capsular species is primarily by wind. The flat seeds are released by waving of the flowering stem and are then collected by ground-dwelling animals. Indehiscent baccate fruits of Yucca sect. Sarcocarpa drop to the ground upon ripening. The fleshy fruits of Y. aloifolia are eaten by mockingbirds (H. Webber 1895). The shed dry fruits of Y. brevifolia are considered to be wind-dispersed "tumble-fruits" (Trelease 1893).

Phytochemistry. Steroidal saponins occur throughout the family, sometimes in high amounts. About 30 sapogenins have been identified, among which hecogenin, tigogenin, and sarsapogenin abound. Sapogenin concentration is often very high in the seed (Wall et al. 1957; Blunden et al. 1978).

Yucca glauca seeds contain linoleic acid. Cyano-genic compounds are reported in Yucca and chelidonic acid in Agave and Yucca (Ramstad 1953). The presence of flavonoids as kaempferol xyloside is reported from Polianthes tuberosa (El-Moghazy et al. 1980) and from Agave americana as kaempferol-3-glucoside and kaempferol-3-rutinoside (Subramanian and Nair 1970). Seed protein electrophoresis is useful in the identification of sections and species in Yucca (Smith and Smith 1970). Wall et al. (1957) did not find alkaloids or tannins in Agave and Yucca.

  1. Genera of three tribes remain in the family following the narrower circumscription (Ojeda and Ludlow-Wiechers 1995): the Yucceae with the hypogynous genera (Yucca, Hesperaloe), the Agaveae with the epigynous, evergreen-leaved and fibrous-rooted genera (Agave, Furcraea, Beschomeria), and the Poliantheae composed of the epigynous genera with soft leaves and a storage rhizome (Manfreda, Polianthes, and Proch-nyanthes). Athough the distinction between the hard xerophytic Agaveae and the softer, mesic Poliantheae is ecologically useful, molecular data do not support the latter division (Eguiarte 1995). The separation between the hypogynous and the epigynous genera is confirmed by recent molecular and cladistic analysis (Eguiarte 1995; Hernandez 1995).
  2. The family Agavaceae was resurrected by Hutchinson (1934) to include six tribes of xerophytic genera of mainly arborescent habit previously included in the Liliaceae and Amaryllidaceae. In the current restricted concept of the Agavaceae, only New World genera with bimodal karyotypes are included. Huber (1969), as well as Dahlgren et al. (1985), segregate Old World genera previously included (e.g., Phormium, Dracaena, Cordyline, Doryanthes) and the New World Nolineae as several other families. All of these families are included in the Asparagales, a segregate from the Liliales. In addition to the karyotype, anatomical, palynological, embryological and fruit characters, and geographical distribution support the new circumscription. The Agavaceae are composed of specialized genera adapted to arid habitats and advanced pollinators. It has been proposed that the more mesic genera may be the result of dedifferentiation from xerophytic types (Alvarez 1990).

Molecular studies of the chloroplast gene rbct indicate that the Agavaceae sensu stricto are a clade within the Asparagales (Eguiarte 1995). The rbcL studies, as well as analysis of chloroplast DNA restriction sites (Bogler and Simpson 1995) and of internal transcribed spacers of nuclear ribosomal DNA (Bogler 1995) strongly support a clade for Agavaceae sensu stricto, with capsular fruits and phytomelan in the seed, separate from the Nolinaceae, which lack phytomelan and are grouped with genera with berries or dry berrylike fruits. All of these molecular studies, as well as cladistic analyses of morphological characters, indicate Hosta (Funkiaceae) as a sister group to Agavaceae, perhaps closest to Yucca (Hernandez 1995). Within the Agavaceae there are two well-

supported dades: Yucca and Hesperaloe with ovaries superior, and Agave, Manfreda, Polianthes, Prochnyanthes, Furcraea, and Beschomeria with ovaries inferior. Furcraea and Beschomeria are closely paired in all cladistic studies and form a sister group to Agave and the herbaceous genera.

Distribution, Habitats, and Ecology. The Agavaceae are centered in SW USA and Mexico, but range from central USA to Panama, the Caribbean Islands, and northern montane S America (García-Mendoza and Galván 1995). Yucca has the widest range, followed by Agave and Manfreda. All genera except Furcraea occur primarily north of Guatemala. Furcraea is the main representative in S America. Several genera are naturalized in the Old World.

Ecologically, the Agavaceae range from xeric to mesic conditions from sea level to 2500 m. They are characteristic in desert and chaparral communities with Larrea, Prosopis, Fouquieria, and cacti. In mesophytic habitats they occur in open, well-drained sites such as cliffs and ravine slopes, usually on limestone-derived soils. Species of Polianthes, Prochnyanthes, and some Agave and Manfreda occur in montane pine-oak forest. Species of Agave and Yucca may be epiphytic in wet forests.

The Agavaceae are well adapted to dry environments and show high efficiency of water use (Nobel 1988). Crassulacean acid metabolism has been reported for all Agave spp. studied and some species of Yucca. Only some species are cold-tolerant

Vesicular arbuscular mycorrhiza have been found in association with Yucca valida (Rose 1959). Various generalized and specific viral and fungal pathogens have been identified on Agave, Yucca, and Furcraea (Wellman 1977).

Several insects are specific to the Agavaceae. Among Lepidoptera, one family, Megathymidae, are exclusive feeders upon Agavaceae, with larvae of particular species feeding in stems or leaves of one or several preferred plant species (Freeman 1969). Larvae of single species in other moth genera also feed preferentially on seeds of Agavaceae (Powell and Mackie 1966).

Paleobotany. Tidwell and Parker (1990) described an arborescent monocotyledon, Protoyucca shadishii, from the Middle Miocene of Nevada. Although the authors did not assign this fossil to a family, they treated it as being closely related to Yucca.

Economic Importance. Members of the Agavaceae have been extensively used by Aztec and other aboriginal New World civilizations (Castetter et al. 1938; Bell and Castetter 1941; J. Webber 1953; Trueblood 1973; Verhoek 1978b; Gentry 1982). They provide fiber from leaf and peduncle, food from flowers and baked stem and leaf bases, beverages, soap, various medicines, ornamentals, and animal fodder. Agave spp. are cultivated for cordage fibers (A. fourcroydes, henequen; A. sisalana, sisal), for the making of distilled alcoholic beverages (primarily A. tequilana), and as a source of corticosteroid precursor hecogenin (A. sisalana) (Cruz et al. 1985). The long narrow fiber cells of Hesperaloe and Yucca can be used as pulped fibers for specialty papers (McLaughlin and Schuck 1991). Yucca has been used for fiber and soap, and provides a wetting agent in fertilizers and frothing agent in drinks and fire extinguishers. Polianthes tuberosa is cultivated commercially as a cut flower and in perfumery. Members of most genera are horticultural subjects.

Key to the Genera

1. Ovary superior 2

- Ovary inferior 3

2. Flowers globose to broadly campanulate; filaments pubescent or papillose, clavate, or stout at middle I. Yucca

- Flowers narrowly tubular to rotate-campanulate; filaments glabrous, subulate-filiform 2. Hesperaloe

3. Leaves tough, long-lived; marginal teeth often corneous; roots arising from stem base 4

- Leaves soft; marginal teeth soft; roots arising from an upright rhizome ("rootstock") 6

4. Leaf apex a long, hard spine; flowers erect or horizontal; filaments exserted 6. Agave

- Leaf apex short or soft; flowers pendulous; filaments included 5

5. Floral bracts small; perianth campanulate; filaments swollen below, narrowed above 7. Furcraea

- Floral bracts large; perianth funnel-shaped; filaments slender 8. Beschorneria

6. Flowers single at nodes, greenish or brownish (rarely white or pink); stamens and style exserted; stigma trigonous or rarely 3-lobed 3. Manfreda

- Flowers usually paired at nodes, white to reddish; stamens and style included; stigma with 3 reflexed lobes 7

7. Leaves chartaceous; perianth tube narrow below, campanulate above, abruptly bent near middle 4. Prochnyantkes

- Leaves herbaceous; perianth narrow, straight or slightly curved 5. Polianthes

Genera of Agavaceae I. Yucca L.

Yucca L., Sp. Pl.: 319 (1753); McKelvey, Yuccas of the SW United States 1, 2 (1938, 1947), rev., Webber, J.M. 1953.

Yuccas of the Southwestern United States. Agrie. Monogr.

U.S.D.A. 17: 1-97. Hesperoyucca (Engelm.) Baker (1892). Clistoyucca (Engelm.) Trelease (1902). Samuela Trelease (1902).

Caespitose or arborescent, stems usually branched; leaves pliant to rigid, margins entire, filiferous or serrulate, spine-tipped; inflorescence a raceme or panicle; flowers white or greenish, globose to campanulate; tepals free or basally united; filaments fleshy, clavate, or slightly swollen, pubescent or papillose; anthers small; ovary superior; stigmas 3 or 1 and capitate; fruit loculicidally or septicidally dehiscent or indehiscent. About 40 spp., mainly in arid and semiarid regions from central USA to Mexico and the Caribbean (Y. aloifolia L.; Y. elephantipes Regel in Central America possibly introduced.

Four sections distinguished by McKelvey. sect. Sarcocarpa, western and southern N America, with indehiscent, fleshy, pendent fruits; sect. Clistocarpa, SE and SW USA, with indehiscent, dry fruits; sect. Chaenocarpa, mainly north-central and eastern USA with septicidal (sometimes also loculicidal) capsule; section Hesperoyucca, containing only Yucca whipplei Torrey from California-Baja California, with loculicidal capsules and capitate stigma, is sometimes raised to the generic level. Major morphological and floristic works have retained the species within Yucca, but chloroplast DNA restriction site and rbcL data place it outside of Yucca and more closely related to Hesperaloe (Clary and Simpson 1995).

2. Hesperaloe Engelm.

Fig. 24A-F

Hesperaloe Engelm. in S. Watson, Botany U.S. Geol. Explor 40th Parallel: 497 (1871); Starr, G., Madrono 44: 282-296 (1998), rev.

Acaulescent; caespitose; leaves linear, to 2 m, apex frayed or a hard spine; margins filiferous; inflorescence to 4 m tall, racemose or paniculate with 3-8 branches; flowers fascicled, tubular, campanulate, or rotate-campanulate, greenish white, maroon-streaked, or red to salmon, or rarely yellow; filaments basally inserted, filiform, included; anthers sagittate; ovary superior; stigma only slightly expanded; capsule septicidal. Five spp. and one ssp., Central Texas and N Mexico on both sides of the Sierra Madre Occidental, limestone prairies, mesquite groves, and rocky slopes.

Manfreda J.H. Salisb, Gen. Pi. Fragm.: 78 (1866); Verhoek-Williams, Study of the tribe Poliantheae (including Manfreda) (PhD thesis Cornell Univ. 1975), rev.

Small to medium-sized; rhizome erect with fleshy and fibrous roots; leaves annual, thin or succulent, apex soft to firm, margins entire, papillate, or dentate; inflorescence a spike or raceme; flowers solitary at nodes, erect or horizontal, green, rarely white or pinkish; tube funnel-shaped; filaments straight or bent in bud, exserted; ovary inferior; stigma trigonous or with 3 reflexed lobes; capsule loculicidal. About 26 spp., Texas and northern Mexico to Honduras and El Salvador, in moist to dry sites.

4. Prochnyanthes S. Watson Fig. 241,J

Prochnyanthes S. Watson, Proc. Am. Acad. Arts 22: 457 (1887); Verhoek-Williams, Study of the tribe Poliantheae (including Manfreda) (PhD thesis Cornell Univ. 1975), rev.

Acaulescent, with a fleshy erect rhizome; leaves chartaceous, with a distinct midrib, linear, lanceolate to oblanceolate, narrowed at base, apical point soft, margins papillate to denticulate; inflorescence a lax raceme; flowers paired at nodes; floral tube bent at middle, narrow below, cam-panulate above, white tinged green or reddish; filaments inserted in tube, subulate; anthers oblong; ovary inferior; stigma with 3 reflexed lobes; capsule globose. Only one sp, P. mexicana (Zucc.) Rose, W Mexico, dry, rocky slopes, grasslands, or moist ravines.

5. Polianthes L. Fig. 24K

Polianthes L, Sp. PL: 316 (1753). Bravoa Llav. & Lex. Pseudobravoa Rose

Small to medium-sized; rhizome short, cylindrical, with fleshy roots; leaves 2-15, thin or slightly succulent, linear to lanceolate or elliptic, with a short, soft point; margin entire or minutely papillate; inflorescence a spike or raceme; flowers usually paired at nodes, red, pink, or white; tube narrowly funnel-shaped, straight to curved; filaments included; anthers oblong; stigma with 3 spreading or reflexed lobes; capsule loculicidal. About 14 spp., W and S Mexico, in well-drained, moist sites.

Agave L, Sp. PI.: 323 (1753); Gentry, Agaves Cont. N America (1982), rev.

Small to gigantic; acaulescent or with short trunk, perennial, poly- or monocarpic; leaves thick and fibrous, linear to lanceolate or ovate, with long pungent apex, margins minutely to coarsely toothed, filiferous or entire; inflorescence a spike, raceme, or panicle, to 12 m tall; flowers in pairs or umbellate clusters, erect, usually yellow or greenish; perianth tubular or campanulate; stamens exserted, filaments subulate, anthers oblong; ovary inferior; stigma 3-lobed; capsule loculicidal. About 200 spp., SW USA to W Panama, the Caribbean and Venezuela, mainly arid and semiarid regions. Two subgenera: subgen. Littaea, with spikes or racemes, and subgen. Agave with panicles.

7. Furcraea Vent. Fig. 26B

Furcraea Vent, Bull. Soc. Philom. 1: 65 (1793); J.R. Drumm, Ann. Rep. Mo. Bot. Gard. 18: 25-75 (1907), rev. Orthographic variants: Furcroea, Furcroya, Fourcroya, and Fourcroea.

Plants massive, acaulescent or with trunk to 6 m high; leaves stiff or flexible, fibrous, lanceolate, apex a short firm point, margin entire, denticulate or coarsely toothed; panicle lax, to 13 m tall with long side branches, producing plantlets; flowers in clusters of 2-5, pendulous, campanulate; tepals mostly free, spreading, greenish or white; filaments included, expanded below middle; ovary inferior; style dilated below the middle; stigma capitate or shortly 3-lobed; capsules loculicidal. Perhaps 21 spp., N South America to Peru, extending to east Central Mexico, the Antilles, and E Brazil. Two subgenera: subgen. Furcraea, with firm-textured, marginally spined leaves, and subgen. Roezlia, with flexible leaves and minutely denticulate margins. In great need of revision and field work.

8. Beschorneria Kunth

Beschomeria Kunth, Enum. Pi. 5:844 (1850). Garcia Mendoza, A. Monographfa del género Beschorneria (Master's thesis, UNAM 1987), rev.

Acaulescent; leaves tough, linear-lanceolate, narrowed at base, apex a long, soft point, margins entire or minutely toothed; inflorescence a raceme or few-branched panicle; flowering stem and bracts red, pink, or yellow; bracts long; flowers 25 together in remote fascicles, pendulous; tepals lanceolate, free but connivent into a tube, greenish, yellowish, or red, papillose or puberulous outside; filaments as long as tepals, subulate; anthers oblong; ovary inferior; style as long as or exceeding the stamens, stigma obscurely 3-lobed; capsule loculicidal. Seven spp., Mexico, dry rocky woodland.

Selected Bibliography

Alvarez, A. 1990. El complejo estomático en la familia Agavaceae II. Epidermis adulta. Feddes Repert. 101:113-134.

Alvarez, A., Köhler, E. 1987. Morfología del polen de las Agavaceae y algunos géneros afines. Grana 26: 25-46.

Arber, A. 1925. See general references.

Arnott, H.J. 1962. The seed, germination and seedling of Yucca. Univ. Calif. Publ. Bot. 35:1-144.

Behnke, H.D. 1981. See general references.

Bell, W.H., Castetter, E.F. 1941. Ethnobiological studies in the American southwest. VIII. The utilization of yucca, sotol and beargrass by the aborigines of the American Southwest. Univ. N.M. Bull. #372, Biol. Ser. 5: 3-74.

Blunden, G., Binns, W.W. 1970. The leaf anatomy of Yucca glauca Nutt. Bot. J. Linn. Soc. 63: 133-141.

Blunden, G., Yi Yi, Jewers, K. 1973. The comparative leaf anatomy of Agave, Beschorneria, Doryanthes and Furcraea species (Agavaceae: Agaveae). J. Linn. Soc. Lond. Bot. 66: 157-179.

Blunden, G., Yi Yi, Jewers, K. 1978. Steroidal sapogenins from leaves of Agaveae species. Phytochemistry 17: 1923-1925.

Bogler, D.J., 1995. Systematics of Dasylirion: taxonomy and molecular phylogeny. Bol. Soc. Bot. Méx. 56: 69-767.

Bogler, D.J. Simpson, B.B. 1995. Chloroplast DNA study of the Agavaceae. Syst. Bot. 20: 191-205.

Boyd, L. 1932. Monocotylous seedlings: morphological studies in the post-seminal development of the embryo. Trans. Proc. Bot. Soc. Edinb. 31:1-224.

Bundrant, L.H. 1985. Poliatithes tuberosa and its hybrids. Herbertia 41: 55-60.

Castetter, E.F., Bell, W.H., Grove, A.R. 1938. Ethnobiological studies in the American southwest. VI. The early utilization and the distribution of Agave in the American Southwest. Univ. N.M. Bull. Biol. Ser. 5: 1-92.

Catalano, G. 1931. Sulla morfologia delle infiorescenze di Agave. R. Inst. Bot. Palermo, Lavori 2: 99-107.

Clary, K.H., Simpson, B.B. 1995. Systematics and character evolution in the genus Yucca (Agavaceae): evidence from morphology and molecular analyses. Bol. Soc. Bot. Méx. 56: 77-88.

Cruz, C., Castillo, L., Robert, M., Ondarza, R.N. (eds.) 1985. Biología y aprovechamiento integral del henequén y otros agaves. Centro de Investigación Científica de Yucatán, A.C.

Davis, G.L. 1966. See general references.

Diggle, P.K., DeMason, D.A. 1983. The relationship between the primary thickening meristem and the secondary thickening meristem in Yucca whipplei Torr. I. Histology of the mature stem. II. Ontogenetic relationship within the vegetative stem. Am. J. Bot. 70: 1195-1204,1205-1216.

Dodd, R.J., Linhart, Y.B. 1994. Reproductive consequences of interactions between Yucca glauca (Agavaceae) and

Tegiticulayuccasella (Lepidoptera) in Colorado. Am. J. Bot. 81: 815-825.

Eguiarte, L.E. 1995. Hutchinson (Agavales) vs. Huber y Dahlgren (Asparagales): análisis moleculares sobre la filogenia y evolución de la familia Agavaceae sensu Hutchinson dentro las monocotiledóneas. Bol. Soc. Bot. Méx. 56: 45-56.

Eguiarte, L., Búrquez, A. 1987. Reproductive ecology of Manfreda brachystachyOy an iteroparous species of Agavaceae. Southwest Nat. 32: 169-178.

El-Moghazy, A.M., Ali, A.A., Ross, S.A., El-Shanaway, M.A. 1980. Phytochemical studies on Polianthes tuberose L. Fitoterapia 51: 179-181.

Erdtman, G. 1969. Handbook of palynology. New York: Hafner.

Freeman, H.A. 1969. Systematic review of the Megathymidae. J. Lepid. Soc. 23, Suppl. 1.

García-Mendoza, A., Galván, R. 1995. Riquezas de las familias Agavaceae y Nolinaceae en México. Bol. Soc. Bot. Méx. 56: 7-24.

Gentry, H.S. 1982. Agaves of Continental North America. Tucson: University of Arizona Press.

Gentry, H.S., Sauck, J.R. 1978. The stomatal complex in Agave: groups Deserticolae, Campaniflorae, Umbelliflorae. Proc. Calif. Acad. Sei. 41: 371-387.

Gómez-Pompa, A., Villalobos-Pietrini, R., Chimal, A. 1971. Studies in the Agavaceae. I. Chromosome morphology and number of seven species. Madroño 21: 208-221.

Granick, E.B. 1944. A karyosystematic study of the genus Agave. Am. J. Bot. 31: 283-298.

Grove, A.R. 1941. Morphological study of Agave lechuguilla. Bot. Gaz. 103: 354-365.

Guttenberg, H. von, 1968. Der primäre Bau der Angiospermen wurzel. Handb. Pflanzenanat. 2nd edn. 8: 134-137, 318333.

Hernández, L. 1995. Análisis cladístico de la familia Agavaceae. Bol. Soc. Bot. Méx. 56: 57-68.

Heslop-Harrison, Y., Shivanna, K.R. 1977. The receptive surface of the angiosperm stigma. Ann. Bot.(Lond.) 41:12331258.

Howell, D.J. 1979. Flock foraging in nectar-feeding bats: advantages to the bats and to the host plants. Am. Nat. 114: 23-50.

Howell, D.J., Roth, S. 1981. Sexual reproduction in agaves: the benefits of bats; the cost of semelparous advertising. Ecology 62: 1-7.

Huber, H. 1969. See general references.

Hutchinson, J. 1934. The families of flowering plants, vol. 2. London: Macmillan.

Joshi, A.C., Pantulu, J.V. 1941. A morphological and cytologi-cal study of Polianthes tuberosa Linn. J. Indian Bot. Soc. 20: 37-71.

Lock, G.W. 1969. Sisal, 2nd edn. London: Longmans, Green.

McKelvey, S.D. 1938,1947. Yuccas of the Southwestern United States, parts 1 & 2. Jamaica Plain, Massachusetts: Arnold Arboretum of Harvard University.

McLaughlin, S.P., Schuck, S.M. 1991. Fiber properties of several species of Agavaceae from the Southwestern United States and Northern Mexico. Econ. Bot. 45:480-486.

Mogensen, H.L. 1970. Megagametophyte development in Agave parryi. Phytomorphology 20:16-22.

Nobel, P.S. 1988. Environmental biology of agaves and cacti. Cambridge: Cambridge University Press.

Ojeda, L., Ludlow-Wiechers, B. 1995. Palinologia de Agavacee, una contribución biosistemática. Bol. Soc. Bot. Méx. 56:2543.

Powell, J.A., Mackie, R.A. 1966. Biological interrelationships of moths and Yucca whipplei. Univ. Calif. Publ. Entomol. 42: 1-46.

Ramstad, E. 1953. Ober das Vorkommen und die Verbreitung von Chelidonsäure in einigen Pflanzenfamilien. Pharm. Acta. Helv. 28: 45-57.

Richter, K.S., Weis, A.E. 1995. Differential abortion in the yucca. Nature 376: 557-558.

Rose, S.L. 1959. Vesicular-arbuscular endomycorrizal associations of some desert plants of Baja-California Mexico. Can. J. Bot. 59:1056-1061.

Schaffer, W.M., Schaffer, M.V. 1977. The reproductive biology of the Agavaceae: I. Pollen and nectar production in four Arizona agaves. Southwest. Nat 22: 157-168.

Shah, G.L., Gopal, B.V. 1970. Structure and development of stomata in the vegetative and floral organs of some Amaryllidaceae. Ann. Bot. (II) 34: 737-749.

Smith, C.M., Smith, G.A. 1970. An electrophoretic comparison of six species of Yucca and of Hesperaloe. Bot. Gaz. 131: 201-205.

Starr, G. 1995. Hesperaloe-. aloes of the west. Desert Plants 11: 3-8.

Subramanian, S.S., Nair, A.G.R. 1970. Chlorogenin and kaempferol glycosides from the flowers of Agave americana. Phytochemistry 9: 2582.

Takhtajan, A.L. 1982. See general references.

Tidwell, W.D., Parker, L.R. 1990. Protoyucca shadishii gen. et spec, nov., an arborescent monocotyledon with secondary growth from the Middle Miocene of northwestern Nevada, USA. Rev. Paleobot. Palynol. 62: 79-95.

Trelease, W. 1893. Further studies of yuccas and their pollination. Annu. Rep. Mo. Bot. Gard. 4: 181-226.

Trueblood, E.W.E. 1973. Omixochitl - the tuberose {Polianthes tuberosa). Econ. Bot. 27:157-173.

Verhoek, S. 1978a. Floral biology of Manfreda virginica (L.) Rose (Agavaceae) Bot. Soc. Am., Misc. Ser., Publ. 156: 82.

Verhoek, S. 1978b. Huaco and amole: a survey of the uses of Manfreda and Prochnyanthes. Econ. Bot. 32:124-130.

Verhoek-Williams, S.E. 1975. A study of the tribe Poliantheae (including Manfreda) and revisions of Manfreda and Prochnyanthes (Agavaceae). Ph. D. Thesis. Ithaca: Cornell Univ., NY.

Verhoek-Williams, S. 1976. Hybridization in Manfreda and Polianthes. Abstr. of Papers, Bot. Soc. Am., Am. J. Bot, Suppl 63.

Wagner, P. 1977. Vessel types of monocotyledons: a survey. Bot. Not. 130: 383-402.

Wall, M.E., Fenske, C.S., Kenney, H.E., Willaman, J. J., Correll, D.S., Schubert, B.G., Gentry, H.S. 1957. Steroidal sapogenins XLIII. J. Am. Pharm. Assoc. 46: 653-684.

Wattendorf, J. 1976. A third type of raphide crystal in the plant kingdom: six-sided raphides with laminated sheaths in Agave americana L. Planta 130: 303-311.

Webber, H.J. 1895. Studies in the dissemination and leaf reflexion of Yucca aloifolia and other species. Annu. Rep. Mo. Bot. Gard. 6: 91-112.

Webber, J.M. 1953. Yuccas of the Southwestern United States. Agrie. Monogr. U.S.D.A. 17: 1-97.

Wellman, F.L. 1977. Dictionary of tropical American crops and their diseases. Metuchan, NJ: Scarecrow Press.

Wolf, F.T. 1940. Macrosporogenesis and the development of the embryo sac in Yucca aloifolia. Bull. Torrey Bot. Club. 67: 755-761.

Was this article helpful?

0 0
Growing Soilless

Growing Soilless

This is an easy-to-follow, step-by-step guide to growing organic, healthy vegetable, herbs and house plants without soil. Clearly illustrated with black and white line drawings, the book covers every aspect of home hydroponic gardening.

Get My Free Ebook


Responses

  • Eyob
    How do indehiscent yucca baccata capsules disperse?
    9 years ago
  • pamphila
    Is there hecogenin in agave tequilana?
    8 years ago
  • mandy
    How to apply gibberellic acid on polianthes tuberosa?
    8 years ago
  • mike
    Does agave americana have a sagittate leaf base?
    8 years ago
  • natalia
    Why do phormium leaves spiral at the tip?
    8 years ago
  • Rudibert
    What are characteristics and salient features of Agavaceae?
    2 years ago
  • juhana vuorela
    What is the floral formular for the following family Agavaceae?
    1 year ago

Post a comment