Cyatheaceae Kaulfuss, D. Wesen d. Farrenkr.: 119 (1827).
Large to very large, less often medium-sized, terrestrial ferns with short to usually long, erect, slender to robust, apically scaly stem; stele radially symmetric, forming a complicated dictyostele with much scleren-chyma on both sides of the bundles, often with accessory medullary and cortical bundles; the surface often bearing a cover of densely matted adventitious roots, rarely spiny, the leaf scars prominent, often the upper part with petiole base remnants, rarely branched.
Leaves forming a rosette; petioles usually close, stout, short to long, bearing scales often inserted on wart- to spine-like epidermal outgrowths, mostly hairy in addition, the adaxial side flattened to sulcate and, with few exceptions, like the other leaf axes bearing antrorse, septate hairs, laterally with 1 (-3) discontinuous lines of pale pneumathodes; petiole bases sometimes with so-called aphlebiae (see below). Lamina pinnate to (more often) bipinnate (+ pinnatifid), herbaceous to coriaceous, usually large, often oblong or deltoid, truncate at the base or the lower pinnae somewhat to (less often) strongly and gradually reduced; leaf architecture entirely catadromous. Vascularization of the petiole essentially of an abaxial and an adaxial arch of many small bundles, but often with additional series (Fig. 27 A). Rachis adaxially sulcate, the groove usually raised in the middle; additional flanking grooves often present in larger species, with a ± persistent indument of scales and/or hairs, often also warts or spines; adaxial indument as in the petiole. Leaf axes stramineous to tawny, less often dark and polished. Upper pinnae, pinnules, etc., with few exceptions gradually reduced and confluent. Pinnae stalked or sessile, the petiolule often with a dark articulation-like discontinuity at its base or occasionally truly articulate. Pinna rachis adaxially sulcate, the groove raised in the middle, mostly strigose, the groove not continuous with that on the primary rachis. Lamina at least initially scaly and (with few exceptions) hairy, these appendages persistent or not; scales on abaxial side of costae, costules, etc. not rarely bullate and/or pale. Ultimate free divisions ± symmetrical, very often liguliform and to some degree falcate, sometimes roundish, entire to cre-nate or pinnatifid, mostly adnate but sometimes narrowed at the base, sessile, costate. Lower surface sometimes glaucous. Veins issuing from the costae/ costules in a pinnate pattern, catadromous or rarely isodromous, the posterior basal one usually issuing from the costule, often from its base; veins simple or usually (subpinnately) forked, free or, especially in the Cnemidaria group, the basal posterior branches anastomosing in pairs and forming costal arches, their free excurrent branches connivent to the sinus (Fig. 28 A). Costae and costules adaxially raised, mostly strigose. Veins not quite reaching the margin. Sori dorsal on the veins, most often at a fork, round; receptacle strongly to hardly raised, containing a vein branch. Indusium attached round the receptacle base, apically with a small to large opening, in the former case irregularly rapturin at maturity (Fig. 28 D); or more unilateral, attached at the costular side only, small to large and scale-like (Fig. 28 C); or wanting altogether (Fig. 28 E); in a few species of subgen. Sphaeropleris replaced by a group of scales placed round the receptacle base. Sporangia numerous, rather small, with a short, 4-seri-ate stalk, mostly intermingled with pericellular hairs
with or without glandular end cell and occasionally broadened and scale-like at base. Annulus almost vertical, complete, bypassing the stalk; stomium well-developed, consisting of several narrow cells. Spores tri-lete, globose, mostly 64, sometimes only 16 per sporangium.
Characters of Rare Occurrence. Adaxially non-strigose axes up to costules in the Cnemidaria group and a few other species. Vein arches also along the bases of the costules in a few species of the same group. Lamina simple in a single species, C. sinuata Hooker and Grev, from Ceylon. Contracted fertile divisions, sometimes also with revolute lobes, in sect Gymnosphaera. Scandent stems in C. ("Thysano-botrya") biformis (Rosenst.) Copel, which has almost lamina-less fertile segments and whose sterile leaves are also dimorphic, with abortive lamina apex. A prostrate stem in C. colensoi (Hook, f.) Domin (New Zea land), a short-creeping, rhizome-like stem in the E. Asiatic C. hancockii Copel. Constantly and regularly branched stems in C. tuyamae Ohba from the Bonin Is. Anadromous pinnae occur very occasionally in one species or another. Stem branches serving as struts and for vegetative propagation in a few African species (Hallé 1966; Tryon and Tryon 1982).
Anatomy and Morphology. Much work has been done on the family, but only a few species have been thoroughly investigated. The most important studies are by Ogura (1927, 1972), Holttum and Sen (1961), Lucansky (1974), Lucansky and White (1974), Sen (1964), A. F. Tryon and Feldman (1975), Holttum (1957) (scales), Gastony and Tryon (1976) (spores), Gastony 1973 (id.).
The stomata are anomocytic, polocytic, and acyclic-paracytic (van Cotthem 1970). Tindale (1956) drew attention to the pneumathodes on the leaf axes and their taxonomic relevancy. Holttum (1957) first demonstrated the presence of two types of scales, viz. the setiferous type with entire margin and sharply offset marginal hairs (Fig. 27 D, E), and the flabelloid type, without such hairs but with irregularly fringed margins and peltate base (Fig. 27 F, G, H). These scales proved to be much more important for the taxonomy of the family than the indusia on which former subdivisions were based. This was first elaborated by Holttum and Sen (1961) and by R.M.Hyon (1970), who empha
sized the difference between scales with and scales without a terminal seta, structurally margínate vs. non-marginate scales; and the so-called squaminate scales of the Nephelea group (see also Gastony 1973), where some spines form part of a scale, transitions between the organs being present (but see Holttum and Edwards 1983). It is still a matter of contention whether the indusium is homologous with the inner indusium of the Dicksoniaceae or not (A. F. Tryon and Feldman vs. Holttum). The presence of characteristic, so-called cubical cells with crystals on the border of sclerenchy-ma and vascular bundles was described by Holttum and Sen (1961) and adduced as evidence for the close relationship between scaly (Cyatheaceae) and hairy (Dicksoniaceae, Metaxyaceae, Lophosoriaceae) tree ferns; there are further important points of taxonomic similarity.
The peculiar elaminate, capillary, highly branched outgrowths near the petiole base found in a number of species have been called aphlebiae and have attracted much attention (e. g., Goebel 1900; Tardieu-Blot 1941; Conant 1983). There are sometimes transitions to reduced but otherwise normal pinnae (e. g., in C. setosa; see Gastony 1973).
For detailed descriptions of the spores, see especially Gastony (1974, 1979), Gastony and Tryon (1976), and Liew and Wang (1976). The spore structure of the infrageneric groups as recognized by Holttum (in Holttum and Edwards 1983) may be summarized as follows: Subgen. Sphaeropteris: surface plain with coarse, echinate elements or low ridges and granulate-
Fig.28A-G. Cyatheaceae. A Cyathea (Cnemidaria) grandifo-lia, detail of pinna with venation and sori ( x 1). B Cyathea roraimensis, part of median pinna with venation and hemitel-ioid indusia ( x 3). C Cyathea heterochlamydea, hemitelioid indusium ( x 10). D Cyathea crenulata, cyatheoid indusium (x 10). D Cyathea crenulata, cyatheoid indusium (x 10). E Cyathea glabra, indusium none (xlO). F,G Cyathea ca-pensis, sporangium, viewed from two different sides (A from Stolze 1974; B from Holttum and Edwards 1983; C-E from Holttum and Sen 1961; F,G from Holttum 1963)
verrucate with rodlets, rarely foraminate; subgen. Cyathea: sect. Nephelea, surface bearing low, long or short ridges to nearly cristate, not echinate; sect. Cyathea, surface bearing rodlets over a plain or verrucate exospore, rarely foraminate or lacking rodlets; sect Alsophila, surface bearing branched and usually echinate ridges, or rodlets and a granulate deposit over a plain or verrucate surface.
The peculiar surface structure of the group treated as the genus Cnemidaria by R. Tryon (1970, etc.) and Stolze (1974), together with the lack of trichomes on the adaxial side of the lamina and the characteristic venation, seem to indicate that it merits recognition as an infrageneric group, a status which Holttum (in Holttum and Edwards 1983) did not accord it. The spores are pitted, usually with three large, equidistant lobes in the equatorial area.
Karyology and Hybridization. Cytologically the family is very homogeneous, with universally n = 69,
Fig. 29. Cyatheaceae. Cyathea excelsa, crowns forming part of canopy of montane forest; La Réunion, Mascarenes. Phot. K. U. Kramer no polyploids and no naturally occurring cases of apogamy being known.
A considerable number of hybrids have been described, some involving different sections (Conant 1975,1983; R.M.Tryon 1976; Holttum 1984), providing additional evidence against recognizing any segregates of Cyathea (see below). Hybridization is supposed to provide a mechanism for speciation, even in the absence of allopolyploidy (Conant and Cooper-Driver 1980).
No hybrids involving parent species from different subgenera have so far been found.
Gametophyte. This was most fully described by Sto-key (1930). Mature prothallia are heart-shaped or occasionally more elongate, with a thick midrib. Peculiar multicellular, usually multiseriate, green hairs occur on both surfaces of older prothallia and offset the family from the Dicksoniaceae where they are lacking. An-theridia are of a primitive, five-celled type with one or two stalk cells. Archegonia are also primitive, with long, rather straight necks. See also Mukherjee and Sen (1986) for further data and for points of similarity with the prothallia of Dicksoniaceae.
Ecology and Distribution. The species are concentrated in the tropics where they are most numerous in montane to (locally) alpine vegetation (Fig. 29). Many species occur in the undergrowth of moist forests, often in ravines; others prefer more open habitats, even swamps, and some grow preferentially in cleared areas (especially species of subgen. Sphaeropteris in Male-sia), where they often form an important constituted of secondary vegetation. Such species are often gregarious, notwithstanding the apparent absence of vegetative propagation (for cases where such propagation has been established, see Hallé 1966 and Brade 1971).
A number of species extend far into south-temperate areas, e.g., in New Zealand and southern South America, but only into very few parts of the north-temperate zone such as India, South China, and southern Japan. Even remote tropical islands usually harbour one or a few, often endemic, species. Continental Africa has only 14 species (Holttum 1981).
Some species are widely distributed, but local endemics are quite numerous, especially on islands and on tropical mountains (Andes, New Guinea). The problem of endemism in tree ferns and its possible origin was discussed by R. Tryon and Gastony (1975).
Few autecological studies on tree ferns have been undertaken, and little is known about the age of individual plants and the longevity of their leaves. Notable exceptions are to be found in Seiler (1981), Tanner
(1983), Holttum and Edwards (1983), and Ortega
Affinity. Formerly the Cyatheaceae were usually associated with the Dicksoniaceae, but this idea was abandoned at Bower's (1926) suggestion. The association was re-established by Holttum and Sen (1961) who even merged the two families, an idea that has not won general acceptance. Metaxya and Lophosoria have been excluded but are usually regarded as related to both. The affinity of Cyatheaceae and Dicksoniaceae is now generally recognized.
Little ist known about affinity to other fern families. Points of resemblance to Thelypteridaceae are thought to reflect affinity (see especially Holttum 1971), but this is again not generally accepted.
Subdivision. The classification into three genera, based on the structure of the indusium, or its absence, was challenged by Domin (1929, 1930, with a predecessor in Copeland 1909), but only gradually abandoned. This author's proposal to recognize only a single genus gained increasing acceptance, although Copeland (1947) still recognized a few minor segregates. Holttum (1955 and later) has only one genus. A system recognizing five genera was recently proposed by Lellinger (1988).
In 1970 R. M. Tryon proposed a new system with six, partly new, partly revived and redefined genera of scaly tree ferns, based in part on the subdivisions of Cyathea sens. lat. as adopted by Holttum (1963). This system was much followed, particularly in America, but rejected by, among others, Brownlie (1969, 1977), Holttum (1977), Kramer (1978), Holttum and Edwards (1983), etc., and again defended by Tryon (1977). Holt-tum's (and others') rejection of Tryon's segregates is followed here, for reasons to be found in the cited papers. The presence of inter"generic" hybrids and the constancy of the chromosome number bear out this treatment (see, e. g., Jermy and Walker 1985). Even a seemingly clear-cut group like Cnemidaria (Stolze 1974), at first also accepted by Holttum (1963), can be delimited only with difficulty, as the limits come out differently whether one lets macromorphological characters or spore characters prevail (cf. Tryon 1970 with Stolze 1974).
The subdivision as given by Holttum in Holttum und Edwards (1983), with two subgenera, Cyathea and Sphaeropteris, mainly based on characters of the petio-lar scales, each subgenus with two sections and a number of subsections, seems the best founded. Some of the subdivisions are constant in indusial characters, other not at all, thus underscoring the unnaturalness of the three "old" genera Alsophila, Hemitelia, and Cyathea, as defined by indusial characters alone. A single genus:
Cyathea J. E. Smith, Mem. Acad. Hirin 5: 416 (1793); Domin (1930); Tindale (1956); Holttum (1954, 1963, 1964, 1965a, b, 1974, 1981, 1982); R.M. Tryon (1976); Brownsey (1979); Holttum and Edwards (1983). Sphaeropteris Bernhardi (1802); R. M.Tryon (1971); Windisch (1977,1978). Alsophila R. Brown (1810); Riba (1967,1969); Conant (1983). Hemitelia R. Brown (1810).
Trichipteris = TrichopterisC. Presl (1822); Barrington (1978).
Gymnosphaera Blume (1828).
Cnemidaria C. Presl (1836); Stolze (1974).
Schizocaena Hooker (1838).
Characters of the family. About 600-650 species, distributed in the warmer parts of the world, lacking in dry areas and largely in the north-temperate zone.
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