50 Osmundaceae

Family 3.

Description

jamaicensis represents the diploid element in this hybrid. A re­port of D. nodosa from Puerto Rico as 116, by Sorsa (1970), ap­parently is an approximate count of another triploid.

Observations New plants are often vegetatively formed from leaves. In D. Wendlandii a bud is initiated at the apex of the rachis (Fig. 8) and a young plant develops from this (Fig. 9). In D. Moritziana the stem becomes thickened and many adventitious roots develop while the young plant is attached to the rachis (Fig. 10). The old rachis often persists after the young plants are well developed (Fig. 11). Nodes are frequent on the petioles (Fig. 11) and have been interpreted as sites of former pairs of pinnae (Brebner, 1902; Underwood, 1909). However, they are spaced differently than the pinnae and their possible function and origin need to be investigated.

Literature

Brebner, G. 1902. On the anatomy of Danaea and other Marattiaceae. Ann. Bot. 16: 517-552.

Presl, C. B. 1845. Supplementum Tentamen Pteridographiae. 119 pp. Pragae.

Sorsa, V. 1970. Fern cytology and the radiation field, in: H. T. Odum, ed., A Tropical Rain Forest, pp. G39-50. Off. Tech. Inform., U.S. Atomic Energy Comm., U.S. Dept. Commerce, Springfield, Virginia.

Underwood, L. M. 1909. Danaea, in No. Amer. Fl. 16: 17-21. Walker, T. G. 1966. Reference under the family.

Osmundaceae

Osmundaceae Bercht. & J. S. Pres!, Pi'irozen. Rostl. 1: 272. 1820. Type: Osmunda L.

Stem erect to decumbent, massive, usually dichotomously branched, or with a single arborescent trunk, medullated pro­tostelic, becoming dictyostelic, indurated, lacking indument; leaves usually ca. 1-2 m long, pinnate, bearing trichomes, at least when young, circinate in the bud, petiole with an ex­panded, stipular base; sporangia separate or in loose clusters, borne on wholly fertile parts of the lamina or on the abaxial sur­face of relatively unmodified segments, with a short, many­rowed stalk, and a poorly differentiated annulus; homosporous, spores with chlorophyll (green). Gametophyte epigeal, with chlorophyll, obcordate to elongate, with a thickened center and thin margins, the archegonia borne on the lower surface in rows along both sides of the thickened portion, the several- to many­celled antheridia mostly on the lower surface of the margins, less often at their edge.

R. M. Tryon et al., Ferns and Allied Plants© Springer-Verlag New York Inc. 1982

Comments on the Family

Osmundaceae 51

The family Osmundaceae has three genera: Osmunda, nearly worldwide, Todea Bernh. of South Africa, New Guinea, Austra­lia and New Zealand, and Leptopteris Presl, an arborescent genus, with filmy leaves lacking stomates, in western Polynesia, New Guinea, Australia and New Zealand.

The Osmundaceae are an old, distinctive family with a fossil record from the Carboniferous. The study by Miller (1971) re­views characters of stems, leaf bases and origin of the roots with the purpose of showing phyletic relationships. The living groups of Osmunda are related to Paleocene species, but some reserva­tion is expressed on allying the older fossils from the Paleozoic to the Cretaceous to the living osmundas. Although there is a relatively rich fossil record, there are still significant gaps that preclude a more complete synthesis of the evolution of the fam­ily. A detailed study of the living species of the family by Hewit­son (1962) includes morphological aspects of the stem and leaves and the anatomy of the leaf base, sporangia and epidermal structure. The disposition of sclerenchyma in the leaf base was regarded as the most reliable anatomical feature for characteriz­ing species and genera.

The Osmundaceae are more advanced than the Ophioglossa­ceae or Marattiaceae on the basis of the sporangium having an annulus and with walls only one cell thick. However, the rela­tively large size of the sporangium, the rudimentary type of an­nulus, and the stipular leaf bases are more primitive characters as compared to those in the families that follow.

The spores of Osmunda and Leptopteris shown in the work of Lugardon (1971, 1972) have a similar massive, rugose exospore, and above this a thin, echinate perispore. The exospore com­pletely envelops the spore as in the Ophioglossaceae and Marat­tiaceae, but does not overlie the scar apex as in those families.

The chromosome numbers are uniformily n = 22 in the fam­ily and they are exceptionally large. The base number is x = 11.

Literature

Hewitson, W. 1962. Comparative morphology of the Osmundaceae. Ann. Mo. Bot. Gard. 49: 57-93.

Lugardon, B. 1971. Contribution a la connaissance de la morphogenese et la structure des parois sporales chez les Filicinees isosporees. 257 pp. These, Univ. Paul Sabatier, Toulouse.

Lugardon, B. 1972. La structure fine de l'exospore et de la perispore des filicinees isosporees. 1. Generalities. Eusporangiees et Osmun­dales. Pollen et Spores 16: 227-261.

Miller, C. N., Jr. 1971. Evolution of the fern family Osmundaceae based on anatomical studies. Contrib. Mus. Paleont. Univ. Mich. 23: 105-169.

52 Osmundaceae

5. Osmunda Figs. 5.1-5.8

Description

Systematics

Osmunda L., Sp. PI. lO63. 1753; Gen. PI. ed. 5, 484, 1754. Type: Os­munda regalis L.

Struthopteris Bemh., Jour. Bot. (Schrad.) 1800 (2): 126. 1802, not Struth­iopteris Scop., 1760 (= Blechnum). Type: Osmunda regalis L (No combi­nations were made).

Aphyllocalpa Lagasca, Garcia & Clemente, Anal. Cien. 5: 164. 1802. Type: Aphyllocalpa regalis (L.) Lagasca et al. = Osmunda regalis L.

Plenasium Presl, Tent. Pterid. 'l09. 1836. Type: Plenasium banksiifolium (Presl) Presl (Nephrodium banksiifolium Presl) = Osmunda banksiifolia (Presl) Kuhn. Osmunda subgenus Plenasium (Presl) Presl, Suppl. Tent. Pterid. 66. 1845.

Osmundastrum (Presl) Presl, Gefassb. Stipes Farm. 18. 1847. Osmunda subgenus Osmundastrum Presl, Suppl. Tent. Pterid. 68. 1845. Type: Osmunda cinnamomea L.

Terrestrial; stem erect to decumbent, often massive, including the persistent petiole bases, lacking indument, covered by long­persistent petiole bases, bearing wiry roots; leaves wholly or par­tially dimorphic, ca. 1-2 m long, with the croziers densely cov­ered by matted trichomes, nearly glabrous at maturity, sterile lamina (or sterile portions) I-pinnate, I-pinnate-pinnatified or 2-pinnate, veins free; sporangia separate, sometimes in loose clusters, borne on wholly to partially fertile, usually 2-pinnate pinnae; spores tetrahedral-globose, trilete, the laesurae ca. ! the radius, the surface coarsely rugose or crested with slender echi­nate processes. Chromosome number: n = 22; 2n = 44.

The stipular leaf bases enclose the stem apex, protecting sev­eral sets of leaf primordia and young croziers. In mature leaves, these bases are laterally expanded and flattened, becoming thin­ner toward the margin (Fig. 4). The fertile pinnae in Osmunda are more complex than the sterile, for example, in O. regalis the sterile pinnae are I-pinnate (Fig. 6), while the fertile pinnae are 2-pinnate (Fig. 3).

Osmunda is a widely distributed genus of six or perhaps a few more species, three American and two of them tropical. There are three species-groups that have often been recognized as gen­era (Bobrov, 1967) or as subgenera: Osmunda-O. regalis and o. lancea Thunb.; Osmundastrum-O. cinnamomea; Plenasium-O. banksiifolia (Presl) Kuhn and o. javanica Blume. Osmunda Clay ton­iana L., sometimes placed with O. regalis and sometimes with O. cinnamomea, is better considered as representing a fourth group.

A long history of intensive morphological and anatomical work on Osmunda has placed undue emphasis on differences within this relatively homogeneous group. The genus is small and while there are distinctive elements within it, they do not ap­pear to represent evolutionary lines as strong as those in other genera of primitive families. Thus an infrageneric classification is not adopted.

Osmunda 53

Fig. 5.1. Osmunda cinnamomea (center) growing with Blechnum serndatum, Lind· saea porloricensis (foreground) and other pteridophytes, Mason river savannah, Clarendon, Jamaica. (Photo Alice F. Tryon.)

Tropical American Species

Tropical specimens of both O. cinnamomea (Fig. 5) and O. regalis (Fig. 6) are usually smaller than those from temperate areas, and tend to have more coriaceous segments, with prominent veins. These and other differences have led to the recognition of sev­eral species that seem to be poorly defined variations of the basic speCies.

Key to Species of Osmunda in Tropical America

a. Fertile leaf with all pinnae fertile, sterile lamina pinnate-pinnatifid. O. cinnamomea L.

a. Fertile leaf with apical fertile pinnae, sterile lamina 2-pinnate. O. regalis L.

Ecology (Fig. 1)

Osmunda is a genus of wet habitats, rarely well-drained situa­tions, most often growing in open habitats but also in shaded woods. In tropical America, plants usually occur in open or brushy habitats which are nearly constantly wet as swamps, bogs,

54 Osmundaceae

Fig. 5.2. American distribution of 05-munda, south of lat. 350 N.

marshes, wet savannahs and lake margins. It may invade wet areas in pasture and meadows, and also occur in shaded habitats in or along streams, on wet brushy banks or wet areas in woods. Plants that develop in suitable habitats form large colonies and may be a few hundred years in age. Osmunda occurs mostly at altitudes from 1000 to 1500 m but there are records as low as 700 m or up to 2000 m and in Uruguay it grows nearly at sea level.

Geography (Fig. 2)

Osmunda is locally but widely distributed throughout most of the world except in cold and arid climates, and in the islands of the Pacific. In tropical America, it is local, often rare and widely scat­tered in central Mexico to Central America, the Greater Antilles to northern Peru, northwest Argentina to southeastern Brazil and south to Buenos Aires in Argentina; also on Bermuda; Os­munda cinnamomea and O. regalis extend northward to eastern boreal North America where O. Claytoniana also occurs.

Spores Studies of spore wall development in Osmunda regalis by Lugar­don (1971) show formation of a massive, rugose exospore. The spore surface consists of a relatively thin perispore with delicate echinate projections overlaying the rugose exospore (Figs. 7, 8). The echinate structures are composed of compacted rods and microbacules that readily become dissociated causing erosion of the perispore. The chemical stability of the spore wall of O. cin­namomea has been shown in the solubility tests of pollen and

3 4

5 6

Osmunda 55

Figs. 5.3-5.6. Osmunda. 3. Sporangia on fertile pinnules, Osmunda regalis, x 10. 4. Stipular petiole bases, O. regalis, x 2. 5. Portion of sterile lamina, O. cinnamomea, Brazil, x 1.5. 6. Portion of sterile pinna, O. regalis, Brazil, x 1.5.

spores by Southworth (1974). Osmunda spore walls were not dis­integrated by hydrolytic acids or inorganic bases, such as 2-aminoethanol, which dissolved sporopollenin in most pollen.

Cytology Cytological records of Osmunda from the American tropics are uniformly n = 22 and correspond to the numerous reports of the genus from temperate and paleo tropical areas. Autotetra­ploid and triploid plants have been experimentally produced by Manton (1950). The tetraploid gametophyte was generally smaller, while cell size of the antheridia, antherzoids and rhi­zoids was larger than in specimens at lower ploidy levels. Karyo­type studies of the Japanese species of Osmunda by Tatuno and Yoshida (1966, 1967) show that the chromosomes are relatively similar except for one pair of submedian B-type chromosomes. On the basis of arm length and satellites the 44 chromosomes can be arranged into five sets of eight and one set of four chro­mosomes.

Observations Biologically Osmunda is one of the most familiar genera of ferns because the species have been utilized in experiments on funda­mental processes. The coiling and uncoiling mechanisms of the

56 Osmundaceae

7 8

Figs. 5.7, 5.8. Osmunda regalis spores. Honduras, Molina 2436. 7. Proximal face, tilted, x 1000. 8. Detail of echinate perispore over the coarsely verrucate exospore surface, x 10,000.

leaves of O. cinnamomea, studied by Briggs and Steeves (1958, 1959) and Steeves (1963), are based on differential cell division and elongation between the abaxial and adaxial regions of the leaf. Auxin produced by the expanding pinnae is an important regulator of the process. The developmental potential of leaf primordia has been studied by Haight and Kuehnert (1969), Ca­ponetti and Steeves (1970) and others. Young excised leaves and primordia isolated from shoot systems in O. cinnamomea show autonomous control of morphogenetic processes.

Osmunda regalis has been utilized in studies of cytological and genetic systems by Klekowski (1973). A large percentage of ga­metophytes of this species were unable to produce embryos. Crossing experiments showed that the failure to form sporo­phytes may be attributed to the presence of recessive lethals. Os­munda regalis was also used for bioassay of stream pollution (Kle­kowski and Berger, 1976); there was a higher mutation rate (chromosome aberrancy) among plants in polluted than nonpol­luted habitats. The plants form large, dichotomously branched stem systems developed from a single zygote. This allows the cal­culation of rhizome growth rate and an estimate of the time of pollution can be made.

A study of the degree of DNA base sequence homology by Stein et a1. (1979) utilized three species of Osmunda. The results indicated that all three species were equally divergent. Spore protein analysis by Petersen and F airbrothers (1971) showed more similarity between Osmunda cinnamomea and O. Claytoniana than either of them to O. regalis. Miller (1967) related O. Clay ton­iana closer to O. regalis, and this agrees with the implied relation­ship of those species as the parents of Osmunda x Ruggii Tryon, the only known hybrid in the family (Tryon, 1940; Wagner et aI., 1977). Considering these different lines of evidence, it is probable that the three species are somewhat distantly related to each other.

Osmunda 57

Literature

Bobrov, A. E. 1967. The family Osmundaceae (R. Br.) Kaulf, its taxon­omy and geography. Bot. Zurn. (Acad. Nauk SSSR) 52: 1600-1610.

Briggs, W. R., and T. A. Steeves. 1958. Morphogenetic studies on Os­munda cinnamomea L.-The expansion and maturation of vegetative fronds. Phytomorph. 8: 234-248.

Briggs, W. R., and T. A. Steeves. 1959. Morphogenetic studies on Os­munda cinnamomea L.-The mechanism of crozier uncoiling. Phyto­morpho 9: 134-147.

Caponetti, J. D., and T. A. Steeves. 1970. Morphogenetic studies on ex­cised leaves of Osmunda cinnamomea: histological studies of leaf devel­opment in sterile nutrient culture. Canad. Jour. Bot. 48: 1005-1016.

Haight, T. H., and C. C. Kuehnert. 1969. Developmental potentialities of leaf primordia of Osmunda cinnamomea. V. Toward greater under­standing of the final morphogenetic expression of isolated set I cinna­mon fern leaf primordia. Canad. Jour. Bot. 47: 481-488.

Klekowski, E. J., Jr. 1973. Genetic load in Osmunda regalis populations Amer. Jour. Bot. 60: 146-154.

Klekowski, E. J., Jr., and B. B. Berger. 1976. Chromosome mutations in a fern population growing in a polluted environment: A bioassay for mutagens in aquatic environments. Amer. Jour. Bot. 63: 239-246.

Lugardon, B. 1971. Reference under the family. Manton, 1. 1950. Problems of Cytology and Evolution in the Pteri­

dophyta. Cambridge Univ. 316 pp. Cambridge, England. Miller, C. N., Jr. 1967. Evolution of the fern genus Osmunda. Contrib.

Mus. Paleont. Univ. Mich. 21: 139-203. Petersen, R. L., and D. E. Fairbrothers. 1971. North American Osmunda

species: A serologic and disc electrophoretic analysis of spore pro­teins. Amer. Mid!. Nat. 85: 437-457.

Southworth, D. 1974. Solubility of pollen exines. Amer. Jour. Bot. 61: 36-44.

Steeves, T. A. 1963. Morphogenetic studies of fern leaves. Jour. Linn. Soc. (Bot.) 58: 401-415.

Stein, D. B., W. F. Thompson, and H. S. Belford. 1979. Studies on DNA sequences in the Osmundaceae. Jour. Molec. Evo!. 13: 215-232.

Tatuno, S., and H. Yoshida. 1966. Karyologische utersuchungen tiber Osmundaceae. I. Chromosomes der gattung Osmunda aus Japan. Bot. Mag. (Tokyo) 79: 244-252.

Tatuno, S., and H. Yoshida. 1967. Karyological studies of Osmunda­ceae. II. Chromosome of the Genus Osmundastrum and Plenasium in Japan. Bot. Mag. (Tokyo) 80: 130-138.

Tryon, R. 1940. An Osmunda hybrid. Amer. Fern Jour. 30: 65-68. Wagner, W. H., Jr., F. S. Wagner, C. N. Miller, Jr., and D. H. Wagner,

1978. New observations on the royal fern hybrid Osmunda x Ruggii Tryon. Rhodora 80: 92-106.