About two thirds of monocot species are adapted to pollination by animals, mostly insects. As in dicots, optical signaling by colorful semaphylls, one of the main secondary attractants, is usually a function of a single or both tepal whorls, but sometimes partly or exclusively provided by exserted filaments (Haemanthus, Xero-nema), staminodes (Cyclanthaceae), or stylodia (Iris). These showy flowers will here be termed phaneranthous. Aggregates of phaneran-thous florets form conspicuous pseudanthic capitula in Aponogeton ranunculiflorus (Dahlgren et aL 1985), some Zingiberaceae [Etlingera (Achasma)], entomophilous Cyperaceae (e.g., Dichromena), umbels in Cirrhopetalum, or geminate pseudanthia in Thalia. However, several groups of monocots bearing small, inconspicuous, and mostly greenish tepals (aphananthous flowers) are animal-pollinated as well (p. 45). They rely on chemical attraction alone, or their visual advertisement is taken over by adjacent, conspicuous extrafloral organs, mainly colored bracts such as the spathes of most members of Araceae, many palms, and the Cyclanthaceae. Also in phaneranthous flowers or inflorescences, visual advertisement may be reinforced by showy bracts, as in Taccaceae, in genera of the Amaryl-lidaceae (Haemanthus spp.), Commelinaceae (Cochliostema, Coleotrype), orchids, Zingiberales, and Bromeliaceae, or by sterile flowers as in Muscari and Oncidium heteranthum. Petaloid involucral bracts form part of pseudanthia in Eriocaulaceae (Paepalanthus subg. Xeractis, Syngonanthus), Etlingera (Phaeomeria), and Androcymbium.
Contrasting nectar guides in form of single spots or patches of fine dots are mainly restricted to Liliales (including Orchidaceae), Iridaceae, Haemodoraceae, Pontederiaceae, and some Zingiberales (Dahlgren and Clifford 1982). Distinct UV-absorbing patterns, invisible to man, have been detected in species of Hemerocallis, Eichhornia, Wachendorfia, and Dendrobium, among many others (Biedinger and Barthlott 1993).
The pigments involved in flower colors, both chymochromic (vacuole soluble) and plas-mochromic (plastidal), are generally similar to those in dicots. Anthocyanins are responsible for most blue, red, and purple colors, and certain anthocyaninidin moieties and types of glyco-sylation have been found only in monocots. For example, a complex compound consisting of six delphinidin and six flavone molecules bound to two atoms of magnesium causes the bright azure tint of Commelina coelestis. Three pigments consisting of rutinosides and diglucosides bound in various positions to cyanidin are responsible for the scarlet coloration of bird-pollinated Bromeliaceae, whereas pelargonidin, the antho-cyanidin which is commonly responsible for this hue, is infrequent in this family. Cyanidin-3-rutinoside also contributes to the maroon coloration of araceous spathes and appendices
(Harborne and Williams 1995). The red pigment haemocorin (9-phenyl phenalenon derivative) present in all vegetative parts of Haemodoraceae is also involved in flower pigmentation in this family (Simpson 1990). Carotene plasmochromes are the coloring matter in many orange-red bird-pollinated corollas, and the orange stylodia of Crocus are unique in containing crocetin, a glycosylated carotenoid dissolved in the cell sap.
b) Olfactory Attraction
Production of floral scents as a means of secondary attraction is widespread in monocots, the fragrances of Convallaria, Hyacinthus, and Polyanthes being familiar as among the most powerful. While fragrance is normally produced on the entire surface of the perigone, it may be localized at particular sites, serving as local scent cues, e.g. on the paracorolla of Narcissus and the labellum of Platanthera. A unique case of olfactory (and visual) floral dimorphism is exhibited by Dimorphorchis lowii, whose spikes bear basally 12 long-lived yellow flowers producing scent, and distally a number of purple nonscented flowers, both kinds of flowers apparently being' fertile (Winkler 1906; pers observ.).
Anatomically and morphologically distinguished scent glands, (osmophores) are found in the staminate zone of the spadix or its sterile appendix in many myiophilous and cantharophilous aroids, where the volatilization of foul or pungent . benzoloid odors is often reinforced by thermogenesis. In Cryptocoryne and Lysichiton the spathe is the odoriferous part. Club- or tail-shaped osmophores are frequent in the pleurothallidine, dendrobiine, and chloraeine alliances of orchids and probably in Burmanniaceae (Vogel 1990). Osmophores which exude liquid odorous substances are characteristic of four subtribes of epidendroid orchids and some aroids, where the fragrance - a blend containing up to 60 different compounds - functions as a secondary as well as a primary attractant. These aromas are gathered and stored as a reward by euglossine bees (p. 43).
c) Corolla Shapes
Apart from signaling functions, the perianth serves as a landing platform, a guide leading animals to feeding positions appropriate for pollination, and if the nectar is concealed (euphilic flowers), to restrict the access to specialized, tongued visitors. Nectariferous flowers and flowers merely pretending presence of nectar (many orchids, p. 43) have three-dimensional, cup-shaped, campanulate, or tubular perianths (most Liliales including orchids, many Asparagales, the Bromeliaceae, Velloziaceae, and Zingiberales). The molding of the corolla, however, is generally less elaborate as compared to the personate, gullet, and spurred corollas of sympetalous dicots. This may be due to morpho-genetical limitations of the tepal whorls, related to their origin from bracts.
The orchid labellum, which often alone substitutes for a gullet, labiate, or spurred flower, is an exception by its greater flexibility. This could be related to a possible complex nature and mor-phogenetic reorganization of the organ, if it is supposed to be a fusion product of a tepal with adjacent staminodes (Endlicher 1836/40, discussed by Endress 1994). The labellum is formed by the posterior, median tepalum of the inner whorl, and not the anterior median tepalum of the outer whorl, perhaps because of the limited evolutionary potential of the latter. In order to bring the median endotepalum to its functional anterior position, the flower undergoes resupination. In a few orchids only, such as species of Disa and relatives with a reduced labellum, it is the posterior exotepalum that forms a spur. Here, since an erect position of the gynostemium would hamper access to the spur's entrance, the column is truncate and the anther tilted backwards (Vogel 1959; Dressier 1992).
The perigone as a whole is rarely integrated into elaborate guiding sculptures, and congenital fusion (syntepaly, or, better, symperianthy; Guedes 1979) is uncommon. Although the perigone is often fused at the base, the dilated apical part is only rarely fused. This may be due to morphogenetic problems in bridging two whorls of phyllomes, or even bridging the distance between the three members of the same whorl -contrary to the situation in the pentamerous, single-whorled dicot corolla. Advanced novel acquisitions such as the paracorolla of Narcissus, on the other hand, may form perfect "bell flowers" (as in N. bulbocodium). Simple syntepalous tubular corollas with a reduced limb occur in Muscari, Polygonatum, bird-pollinated Liliaceae, Agavaceae, Blandfordiaceae, Amaryllidaceae, and Iridaceae.
Like symperianthy, floral monosymmetry generally remains at an evolutionary level lower than in dicots, again with the exception of the orchids.
In the Iridaceae (Gladiolus, Antholyza, Babiana), zygomorphy, including that of guide marks, is known to be determined by gravity (geomorphosis). Development of regular corollas results when such plants are kept on a clinostat. The arcuate bending of stamens and the style, frequent in Liliales and Asparagales, and facilitating sternotribic or nototribic pollination, is also a geomorphosis. In Anigozanthos, unilabiate zygomorphy is produced by a secondary ventral splitting of a congenitally united corolla tube. Zygomorphy, in most cases innate, is a family character of the Orchidaceae, Corsiaceae, Phily-draceae, Pontederiaceae, Musaceae, Heliconia-ceae, Strelitziaceae, and Lowiaceae. The radial flowers of Iris and Moraea consist of triads of zygomorphic units. Each unit is made up of a tepal of the outer whorl and a petaloid stylodium, and is functionally equivalent to a zygomorphic nototribic flower. In Cypella and relatives, the lips formed by the inner whorl.
The phaneranthous perigone (which itself is reduced and sepaloid) is replaced by petaloid staminodia and their fusion products in four zingiberalean families. Especially in the ginger family and Costaceae, perfect gullet and personate flowers have evolved, paralleling in shape those of orchids. The complete loss of intrafloral symmetry in the flowers of the Marantaceae and Cannaceae is utilized in building a highly advanced pollination apparatus. Individual flowers are integrated into a higher level of symmetry, whose plane is displaced outside the flower, governing a partial inflorescence, as in the pollination unit of Thalia, which consists of a pair of mirror-image asymmetric flowers.
d) Pollination Mechanisms
Many modes of pollen exposure known from the dicots recur in the monocots. The usually 6 or 3 stamens may be enclosed in the corolla (Muscari, Polygonatum, Galanthus) or, at the other extreme, be long exserted and often possessing versatile anthers, especially in brush-type flowers of collectively pollinated inflorescences as in Agave, Xeronema, Haemanthus, Massonia, Xanthor-rhoea, Encholirium, Dasypogon, etc. Zygomorphic arrangements of upcurved or downcurved stamens are associated with sternotribic (e.g., Hippeastrum, Hemerocallis) or nototribic (e.g., Gladiolus) pollination. Pollen production may extend over a couple of days as stamens successively rise into functional positions and dehisce (e.g., in Alstroemeria). In many Iridaceae and in Veratrum with regular flowers the stamens converge, forming a central group with extrorse anthers. Extrorse anthers also occur in nototribic meranthia (Iris) and are characteristic of the Alismatales, Araceae, and Triuridaceae. Introrse anthers occur throughout the Asparagales (except Ruscaceae), Cya-nastraceae, Zingiberaceae, and Orchidaceae. In other families, both anther types occur, in accordance with the intended positioning of visitors. In the basically diplostemonous androecium reduction of stamen number, enhancing pollen economy and concomitant precision of pollen deposition is common. Flowers with 3 stamens are common; reduction to two stamens is found in the Cypripediaceae, while a single fertile stamen is left in Orchidaceae, Philydraceae and Zingiberaceae. In Marantaceae and Cannaceae only a half anther is fertile. Because a fail-safe attachment of pollen upon the visitor's body is crucial in these monantherous flowers, sticky secretions of the stigma or its derivatives (rostellum) in orchids, Marantaceae, Cannaceae, and Etlingera, or mucilage produced by the connective (Hedychium, Alpinia) are instrumental in the pollination mechanism, serving to attach pollen masses firmly on the visitor (Vogel 1984).
Marantaceae and Cannaceae are precociously protandrous, the pollen being deposited on the style's surface in the bud. Functionally, the flowers are homogamous. The style of the Marantaceae is sensitive (Kunze 1984) and snaps down forcibly when touched; in the course of this single stroke, it (1) scrapes off from the visitor, with a sharp edge, any pollen it carries, (2) loads the stigma with this pollen, (3) smears, by means of a stylar gland, an adhesive upon the visitor, and (4) deposits fresh pollen thereupon. The process is irreversible, and the first and only efficient visitor delivers the pollen it carries and picks up new pollen (Kennedy 1978; Kunze 1984; Vogel 1984; Classen-Bockhoff 1991). Resinous secretions of the spatha or pistils mediate application of loose pollen accumulated at the bottom of the spathe in some Araceae (Monstera, Ramirez and Gomez 1978; Philodendron, Gottsberger and Amaral 1984). Secondary pollen deposition is also recorded in some Alismatales (Yeo 1993).
Where secondary polyandry occurs in zoophil-ous monocots, it is, with the exception of the Alismatales, usually linked with the syndrome of pollen flowers (p. 42).
The pollen grains of monocots, rather monotonously sulcate or uniporate, generally have less varied exine sculptures than are found in dicots. The exine is comparatively smooth or granulate, in some zoophilous taxa (but also in Lemna) it is spinulose; in most Zingiberales, for example, it is very thin or completely lacking. The zoophilous pollen is usually sticky because of tryphine; in Cryptocoryne it is embedded in a sticky fluid and extruded from the anther in creamy masses. Many other Araceae shed dry pollen, which then collects at the bottom of the spathe, and dry pollen is characteristic of the common pollen flower syndrome (p. 42). In most orchids, the anther's pollen content is in compact packets (pollinia), and in many tribes it is transferred in the form of pollinaria by attached, sticky rostellar products (retinacula, viscidia).
Insect-trapping is usually combined with sapro-myiophily or cantharophily and deception. Homogamous flowers of Taccaceae, some Bur-manniaceae, Trichopus, Pentastemona, Conval-lariaceae-Aspidistreae and -Ophiopogoneae, and some orchids (Pterostylis), provide a pollination chamber and are presumed to attract small insects which enter and stay inside more or less deliberately for a short time (semitraps), but detailed observations are lacking. In the strictly dichogamous, protogynous inflorescences of Araceae, all levels of insect-trapping mechanisms are represented, from long-lived semitraps (pollination chambers with insects that come in and go out almost without hindrance), to perfect kettle traps (visitors captive; various exactly timed schedules for retention and release; pollen export and potential import by the same individuals). In the pistillate kettle traps of dioecious Arisaema and female phase spathes of Pinellia visitors are retained until they die. Slippery surfaces and semitraps are found in bee-pollinated Cypripe-dium and Stanhopea.
The predominantly papillate stigmas of monocots are either of the Dry or the Wet type (Heslop-Harrison and Shivanna 1977, see p. 46), in the latter case being covered with a watery or oily secretion. As far as is known, wet or moist stigmas are characteristic of Alstroemeriaceae, Philesia-ceae, Asteliaceae, Orchidaceae, Lomandraceae, and Cyclanthaceae. Groups characterized by dry stigmas include the zoophilous Alismatales, the Calochortaceae, Convallariaceae, Iridaceae, Erio-caulaceae, Philydraceae, Pontederiaceae, Vello-ziaceae, and most of the anemophilous monocots. Both types occur within many other families including Liliaceae, Araceae, and palms (Table 1). Among hydrogamous taxa, there are stigmas of the Dry type as well as stigmas provided with a waterproof adhesive (Amphibolis, Pettitt et al. 1980).
Alismatales with apocarpous polymerous gyno-ecia have as many styles and stigmas as carpels; most syncarpous pistils possess a single style. While in a great many zoophilous taxa the stigma is small, usually topping a slender style and emergent beyond the stamens and thus promoting herkogamy, it is subsessile and often large in the aroids and Cyclanthaceae. It is extremely enlarged and umbrellalike in Tupistra, where it ocdudes the flower entrance, leaving only narrow openings for the access and exit of tiny pollinators. The stigma may be entire or trilobed, while in various Iridaceae it is divided into three stylodia which are repeatedly bifurcate or brightly colored, thus playing a part in visual attraction. In the large, petaloid stylodia forming the upper lips of the herkoga-mous meranthia of Iris the stigma is confined to a movable flap which faces entering bees and receives cross-pollen. As the bee withdraws, the flap is forced upward, hiding its receptive surface, and so selfing is precluded. The stylodia of the Bromeliaceae are flabellate with a dilated papillose, receptive distal rim. The rim, however, is contracted to a small area by plicate or helical foldings (Brown and Gilmartin 1989; Schill et al. 1988).
Dichogamy is widespread and sometimes family-specific. Zoophilous families known to be protogynous include Convallariaceae, Dracaena-ceae, Araceae, and Cyclanthaceae, while more or less proterandrous flowers are typical of Burmanniaceae, Amaryllidaceae, most Iridaceae, Hemerocallidaceae, Bromeliaceae, Melanthiaceae, and Butomaceae. Other families are predominantly homogamous, or (Alliaceae, Asphodela-ceae, Liliaceae, Palmae) exhibit both kinds of dichogamy.
Nectar Flowers. The vast majority of zoophilous monocots have nectar flowers, and only nectar-producing groups have strongly adapted to specialized pollinators and undergone adaptive radiation in floral styles (p. 44). The nectar secreted by monocots is like that of dicots and as to the types of sugar solubles it exhibits no particular trends. Many orchid flowers are nectarless but, by shamming presence of nectar, also belong to this ecological class.
Following the comprehensive study of Daumann (1970), carpellary septal nectaries are both restricted to, and widespread in, the monocots, but are by no means universal in this clade
(see also Schmid 1988). Their alleged occurrence in dicots (in Buxus, Cneorum) has not been confirmed (Daumann 1974), but papillate nectar epi-thelia occur on the carpel flanks of Caltha (Smets and Cresens 1988). There are no nectarial disks in monocots. The notion that the evolution of septal nectaries is a synapomorphy of the monocots is still under debate. Septal nectaries occur in at least one family of each order (Table 1), except for the Triuridales, Arales, Orchidaceae, and the anemophilous orders Juncales, Poales, and Cyperales. In their most primitive condition they are freely exposed at the carpel flanks of apocarpous gynoecia, as in entomophilous Alismatales. They are usually concealed in syncarpous ovaries, lining longitudinal clefts inside the septa and drained via three external outlets that may be situated at the top, in the middle, or at the base of the ovary. The clefts are usually separate, but may also merge centrally, forming a three-winged cleft (Tofieldia, Burmannia, Bromeliaceae, Palmae). In epigynous flowers the septal nectar is discharged distally by peristylar pores at the bottom of the corolla (Amaryllidaceae, Agavaceae, Iridaceae-Ixioideae, Haemodoraceae, Bromeliaceae, Velloziaceae, Cannaceae, Costaceae). In Wachendorfia and Costus, only two septal clefts are developed and nectariferous. In vertebrate-pollinated epigynous flowers with copious nectar secretion, the secretory surface is often displaced to sterile distal or proximal parts of the ovary and here enormously enlarged by labyrinthic ramification, reminiscent of kidneys.' The peristylar nectariferous protrusions of the Zingiberaceae are possibly derived from septal glands.
Anatomically, septal nectaries are epithelial, with secretion oozing from their entire - sometimes (Alliaceae, Themidaceae) papillate - epidermis, which is usually underlain by several layers of storage tissue. Remarkably, the mesenchymatous gland type of nectary, in which nectar discharges via stomatal pores, seems to be missing in mono-cot flowers, while predominant in the disks of dicots.
The nonseptal nectaries found in monocots are usually epithelial and located on the tepals (perigonal nectaries). As far as known, they are restricted to nectariferous Liliaceae, Orchidaceae and Triuridaceae, Calochortaceae, Alstroe-meriaceae, Luzuriagaceae, Melanthiaceae, and Eriocaulon; septal nectaries are absent there. In the Iridaceae, perigonal nectaries characterize the subfamily Iridoideae, while in the Ixioideae septal nectaries are developed (Goldblatt 1990). The nectariferous taxa of tribe Mariceae (Trimezia spp., Neomarica) produce nectar in perigonal gland fields, the gland fields being unicellular hairs. This type seems to be unique in monocots. There are also androecial nectaries (some Hydrocharitaceae and Alismataceae; Colchica-ceae, Hemerocallidaceae, Hanguanaceae, and Cyclanthaceae), and rarely nectaries seated on the back of carpels (Paepalanthusi Aponogetona-ceae?). Finally, in some Araceae the stigma (Arum, spp. of Anthurium) or staminodes (Spathicarpa) exude nectar. All these glands are of the epithelial type.
While in allophilic flowers, which are usually rotate and shallow, the nectar is freely exposed, it is concealed and stored in the depth of the corolla in flowers adapted to specialized (eutropous), tongued or beaked animals. In most cases, the container is a perigone tube. The tube may be extremely elongated and slender in moth-pollinated taxa (Crinum, Hymenocallis, Lapei-rousia, Velloziaceae). In Lilium, Strumaria, and Themidaceae the tube is often subdivided into separate nectar pipes by prominent adnate filament bases that form septa. These compel visitors to probe them consecutively. In Milla three canals run down within an elongate receptacle to a distance of 10cm below the superior ovary, where nectar is secreted. Long tubes, however, are not always nectar pipes exploited by long tongues. Those of Crocus merely conduct the fluid by capillarity from subterranean septal nectaries up to the mouth, where it is taken by bees. In Gethyllis, Colchicum, and some Iris spp., also with underground gynoecia, the long perigone tubes have no other function than to expose the limb above the ground, while those of hydrogamous Elodea and other Hydrocharitaceae raise the limb above the water surface, substituting a pedicel. Also in Weldenia (Commelinaceae) the tube replaces a pedicel. Flowers with perigonal nectaries often present the reward excentrically enough to induce insects to crawl around the (mostly nototribic) sexual organs and to exploit the sources one by one (revolver flowers; Scoliopus, Tricyrtis, Veratrum, Androcymbium). Each nectariferous inner tepal of Neomarica and species of Trimezia has a flexible joint, forming a balance that tilts, when burdened with a probing bee, towards the central sexual column. Nectariferous perigonal furrows — two in Aistroemeria, three in Bomarea and Philesiaceae, and six in Lilium and Gloriosa species — are also designed to be exploited separately. The pendent flowers occurring in the latter two genera are visited by hovering lepidopterans that, while circling the perigone, must introduce their proboscis separately into each furrow. Tricyrtis, Herreriopsis, and Dichelostemma store nectar in three pouches. Nectar-containing spurs are common in orchids but extremely rare outside this family; Disporum calcaratum with three, and Gladiolus (Kentro-siphon) saccatus with a single spur are examples. Scale-like nectar covers ("Saftdecken") on the perigone are found in Vriesea and Barbacenia, fimbriate fringes bordering perigonal nectaries occur in Fritillaria and Calochortus.
Flowers with Other Rewards. Nectarless flowers occur in the abiotically pollinated monocots, but are also widely scattered among the entirely or partially zoophilous orders. In all of these orders there are at least some taxa which lack floral nectaries (Table 1). Save for a few exceptions mentioned above, nectarlessness is widespread in the Arales, while Taccaceae, Tecophilaeaceae, Philydraceae, Commelinaceae, Xyridaceae, Maya-ceaceae, Pandanaceae, Cypripediaceae, and Apostasiaceae are characterized by this feature. In the Dioscoreales, Commelinales, and Bromeliales, nectariferous families form the minority; most remaining zoophilous families have at least some taxa with nectarless flowers. While in several orders, such as Liliales and Asparagales, there may have been secondary loss of nectaries, their possible basic absence in groups like Commelinaceae, Dioscoreales, and Pandanales is still a matter of discussion.
Pollen Flowers. These represent the most important zoophilous syndrome involving absence of nectar. They are exclusively melittophilous and offer pollen as the reward to female bees that gather it as a provision for their larvae. They generally have flat or bowl-shaped corollas and freely exposed, conspicuous, usually yellow anthers. Usually being oligandrous, the monocots are restricted in producing a sufficient amount of surplus (fodder) pollen. A few genera have evolved secondary polyandry: Gethyllis, Vellozia, bee- and beetle-pollinated palms, Cyclanthaceae, and certain ento-mophilous grasses. However, most pollen flowers have enlarged the volumen of their six, three, or (Philydraceae) even the single anther. Flowers of this type (Solanum type, Vogel 1978; Faegri 1986) are predominantly actinomorphic, pendent, and their enlarged poricidal anthers are connivent, forming a central cone around a protruding style; they produce copious loose pollen that is discharged by vibration (buzzing). The Tecophilaeaceae, various Lomandraceae Echean-dia, Sowerbaea, Calectasia, Apostasia, and
Galanthus belong here. In other pollen flowers, the androecium is more or less spreading, sometimes with poricidal anthers and dry pollen (Dianella, Thysanotus, Rapateaceae), sometimes with longicidal anthers and ± sticky pollen (Narthecium, Chlorophytum, Arthropodium, Stypandra, Libertia, Hypoxydaceae, Xyridaceae, Commelinaceae pp.). Stamen dimorphism of pollen flowers with conspicuous fodder anthers and fertilization anthers (often with cryptically colored pollen) (heteranthery), occurs in the monosymmetric flowers of Cyanella, Monochoria, and several genera of the Commelinaceae. Certain oligandrous pollen flowers pretend more copious reward than is really available by shamming pollen or additional anthers (partial deception). Yellow-colored pollen dummies are produced by sterile anthers (Commelina, Murdannia), anther or filament appendages (e.g., Dianella, Arthropodium, Dichopogon) or hair tufts associated with true anthers (Coleotrype and other Commelinaceae, Bulbine, Narthecium, Tricoryne, Xyris).
Oil Flowers. The flowers of a small number of nectarless monocots secrete a fatty oil, which is collected by specialized anthophorid bees for brood rearing and probably for lining the walls of their underground brood cells. The taxa involved are all neotropical. The liquid is produced by special glands (elaiophores); these are sometimes arranged in pairs, as the oil is always scraped by the legs. The elaiophores consist of glandular hairs on the tepals or filament columns in species of Sisyrinchium, in various genera of the iridaceous tribe Mariceae, and in at least four genera of subtribe Ornithocephalinae (Orchidaceae). In species of Maxillaria, Oncidium, and in Sigma-tostalix, the lipid is produced by warty epithelia of the labellum (Vogel 1974).
Food Tissues. Starchy tissue forms another edible reward; in several beetle-pollinated aroids either the interior flank of the spathe, spent male (lowers (and pollen), or staminodes are regularly gnawed by pollinating coleopterans; some of them even breed in the decaying inflorescences, lidible flower parts of Cyclanthaceae and palms are eaten or used for oviposition mainly by weevils (Curculionidae) which transfer the pollen. The fleshy, colored bracts next to the floral spikes of Freycinetia (Pandanaceae) are not only a visual attractant, but also provide food for vertebrates: predominantly birds in ornithophilous, u nd mainly flying foxes in chiropterophilous species.
Housing. The presentation of sleeping holes for bees as a reward in flowers of Serapias appears to be unique in flowering plants (Dafni et al. 1981; Paulus and Gack 1994). The inflorescences of beetle-pollinated palms, Cyclanthaceae, and aroids also provide shelter for their visitors, a feature that may play a functional role.
Perfume Flowers. This melittophilous, entirely neotropical floral syndrome is characterized by the production of powerful spicy volátiles which are exuded in small droplets on the glandular surface of flower parts. It is only male bees of the family Euglossini that are attracted and pollinate these flowers. They collect the aromas which consist of specific mixtures of terpenoids, benzoids, hydrocarbons, etc., by brushing the glands with their front legs. The males use the exudate as a pheromone in their mating display in a way which is still incompletely explored (Vogel 1966; Dressier 1992; Williams and Whitten 1983). The orchid tribes Catasetinae, Stanhopeinae, and Lycastinae, altogether with ca.625 species in 55 genera, produce such liquid perfumes as an attractant and reward, in some genera combined with most sophisticated sliding and catapult mechanisms. In monocots, the perfume syndrome is also known from Spathiphyllum and spp. of Anthu-rium. In addition, scent collecting has been observed in Xiphidium (Haemodoraceae).
f) Floral Deception
Totally deceptive flowers that are devoid of any real reward are disproportionally common. They are found in up to half of orchid species; this family includes 34% of all monocot species. The presence of both nutritive and non-nutritive rewards may be simulated (Vogel 1993). Among the former, false nectar flowers prevail; bees or birds visit them. The empty floral spurs of Orchis and Dactylorhiza are classical examples, already recognized by Sprengel (1793). Deception of bee females by false pollen occurs in species of Maxillaria and Polystachya. Most sapromyio-philous monocots (see Table 1) simulate nutritive rewards or even brood sites; both color and smell help elicit instinctive attempts at oviposition in dipterans (some flowers secrete small amounts of nectar which, however, is not the motive for visitation). Plants with such flowers are found in several tribes of Araceae, many orchids (Pleurothalli-dinae, Bulbophyllinae), Stemonaceae, Taccaceae, Trichopodaceae, Ferraría, Scoliopus, Eucomis, and
Annonaceae, Aristolochiaceae, and Piperaceae, believed to be close to the phyletic roots of monocots, are too specialized anthecologically to suggest a direct link with syndromes found in primitive monocots. However, a strong tendency towards myiophily and cantharophily exhibited by the Dioscoreales, Aspidistreae, Araceae, and Cyclanthaceae may still reflect a trait prevalent in ages when flies andbeetles were the main agents in the floral world. In Araceae, an advancement has since taken place, paralleling trends in the Annonaceae, by incorporating large-sized modern dynastid coleopterans as pollinators (Philodendron and allies, Gottsberger and Silberbauer-Gottsberger 1991). Participation in the beetle-pollinated "poppy guild" (Dafni et al. 1990) by members of Aristea (Goldblatt and Manning 1996) and Tulipa and Calochortus is probably also a relatively recent evolutionary event. Certain complicated myiophilous contrivances of the Burmanniaceae, Taccaceae, and Aspidistra appear to be derived as well. Pollination strategies are rather uniform in the above-mentioned families, and also in anemophilous groups. However, an intensive adaptive radiation into different highly adapted floral styles has taken place within families and genera of the Liliales, Asparagales, Zingiberales, and Velloziaceae. Here the possession of septal or perigonal nectaries has given rise to flowers adapted to the more or less complete spectrum of guilds of tongued, anthophilous insects (myiophily, melittophily, psychophily, sphingophily, phalenophily), and vertebrates (ornithophily and chiropterophily), repeating the functional floral styles of euphilic dicots. Particular adaptations reflect a common history of interaction with endemic vectors. Neotropical Marantaceae (Calathea, Ischnosiphon, Mono-tagma) are adapted to long-tongued euglossine bees, species of Lapeyrousia and Disa from the Cape are associated with long-tongued nemes-trinid and pangonid dipterans; paleotropical Antholyza, Brunsvigia, Strelitzia, Burbidgea, Xeronema, but also the neotropical Puya provide special perches to passerine birds; or geoflory in Etlingera (Achasma) is connected with pollination by birds hopping on the ground. Musaceae, Strelitziaceae, and Cannaceae are almost exclusively characterized by bird, bat or lemur pollination, suggesting a long association with vertebrate pollinators. The hummingbird-adapted flowers so common in bromeliads and in Heliconia must have evolved in more recent, Post-Gondwanian times.
Was this article helpful?