Amer. J. Bot. 62(9): 982-992. 1975. THE GAMETOPHYTES OF OPHIOGLOSSUM PALMATUM L. 1 MICHAEL R. MESLER Department of Botany, University of Michigan, Ann Arbor 48104 ABSTRACT Gametophytes of the epiphytic species Ophioglossum palmatum L. are described for the first time, bringing the number of Ophioglossum species with known gametophytes to 11. Although somewhat unusual in terms of (a) degree of branching, (b) the marked expansion of the basically cylindrical axis in some cases, and (c) production of stout, papilla-like rhizoids, the gametophytes of O. palmatum are more similar to other Ophioglossum gametophytes than they are to the gametophytes of Botrychium or Helminthostachvs. Gametophyte characters do not provide strong evidence for placing O. palmatum into a separate genus, viz., Cheiroglossa. The gametophytes of O. palmatum most closely resemble those of the other epiphytic species in the genus, O. pendulum. This similarity suggests a need for a reevaluation of modern taxonomies which, in general, treat the two species as only distantly related. THE GENUS Ophioglossum sensu lato comprises All previous interpretations of the relationships some 30 species of primarily small, terrestrial, of the members of the genus Ophioglossum s. I. fern-like plants. Only two species occur regularly have been based entirely on the sporophyte. Ga­ as epiphytes. One of these, O. pendulum L., metophytes are known from only 11 species and which extends in the Old WorId tropics from in many cases incompletely (see Boullard, 1963, Madagascar east to the Hawaiian Islands, is char­ for a review of previous reports; also Mahabale, acterized by the production of long, pendant, 1937a, b, c; Mesler, 1972, 1973). Although ribbon-like leaves which are simple or forked as Campbell (1907, 1911) and Lang (1902) de­ many as three times. Each leaf bears a single fer­ scribed the gametophytes of O. pendulum, those tile spike. In contrast, the other epiphytic spe­ of O. palmatum remained unknown until recently cies, O. palmatum L., typically bears several fer­ (Mesler, 1972). The objectives of the present tile spikes per leaf. The leaves of this species study are as follows: ( 1) to provide a detailed have an expanded basal blade region which account of the structure and development of the divides distally into a variable number of lobes. previously undescribed gametophytes of O. pal­ While best represented in the New WorId tropics matum; (2) to present preliminary observations and southern peninsular Florida, O. palmatum on the embryos of this species; (3) to describe has also been reported from Madagascar, Zaire, the natural history of the gametophytes as they oc­ Reunion, the Seychelles, and South Vietnam. cur in southern Florida; and (4) to consider the Divergent concepts of the relationships of the problems of the evolutionary relationships of O. epiphytic species to one another and to the other pendulum and O. palmatum and the taxonomic members of the genus are reflected in differing validity of the genus Cheiroglossa in light of the taxonomic treatments at the generic and sub­ new evidence from the gametophyte generation. generic levels. Whereas some authors have as­ signed O. palmatum and O. pendulum to sepa­ MATERIALS AND METHODs-Collections of ga­ rate genera, Cheiroglossa Presl and Ophioderma metophytes from a single locality in Collier Co., (Blume) Endlicher, respectively, others have Florida, were made in December, 1971, and placed them in separate subgenera, adopting a March, 1972. Although once relatively abundant broader concept of the genus Ophioglossum. At in southern Florida, O. palmatum is now pos­ least one author (Nakai, 1925, 1926) regarded sibly in danger of extinction there (Mesler, them as more closely related to each other than 1974). Previous sanctuaries for the species have to the terrestrial members of the genus and ac­ burned following extensive drainage programs in corded them common generic status under the the area. In addition, the superficial resemblance name Ophioderma (Blume) Endlicher. of O. palmatum to Platycerium (hence the col­ loquial name "dwarf staghorn fern"), coupled 1 Received for publication 24 September 1974. I would like to express my sincere thanks to the fol­ with the distinctive appearance of the species in lowing individuals for their generous assistance: W. H. its own right, has led to vandalism for horticul­ Wagner, Jr., C. E. Delchamps, J. G. Bruce, D. Beale, tural purposes. The species, however, has not R. E. Hair, and J. R. Jennings. I am especially grateful to Professor Wagner for suggesting this research project been successful in cultivation. and for critically reading the manuscript. The population of O. palmatum visited by the 982 October, 1975] MESLER-OPHIOGLOSSUM PALMATUM 983 Fig. 1-5. Ophloglossum palmatum, I. Sporophytes growing on the cabbage palmetto. X 0.18. 2. Fertile spikes at top of the stipe. X 0.75. 3. Rhizoids, surface view (stained). X 80. 4. Entire gametophyte, showing branching confined to essentially a single plane. X 14. 5. Unequal apical division (living, unstained specimen). X 20. author is confined to a mixed hardwood associa­ area has not occurred in recent years. The domi­ tion, occurring along a river in the dwarf cypress nant tree species present are Acer rubrum, Quer­ glades of southern Florida. Although signs of past cus virginiana, Taxodium distichum, and Sabal fire damage are evident, extensive burning of the palmetto. The gametophytes of O. palmatum 984 AMERICAN JOURNAL OF BOTANY [Vol. 62 were found growing in the decaying matter that tered beneath the leaf bases and, upon decom­ accumulates between the imbricate leaf bases of position, they too may add to the organic sub­ the Cabbage Palmetto. After removing portions stratum. The texture and moisture content of this of the tightly held leaf-base armor, individual ga­ substratum varies from relatively moist and com­ metophytes as well as quantities of the substra­ pact to dry, loose, and fibrous. tum in which they were growing were collected. A survey of the population indicated that the The substratum yielded additional gametophytes sporophytes of O. palmatum are not confined to after closer examination in the laboratory. specific zones on the palmettos; instead, plants of Gametophytes were fixed in FPA or medium differing ages were observed at various heights chrome-acetic, the latter solution yielding better along the stems, from 0.5 m-5 m. The roots and histological preparations. Photographs of whole stems of O. palmatum are completely covered by specimens (some of which were surface stained the palmetto leaf-base mantle; only the some­ with iron hematoxylin, following a procedure de­ what fleshy, lobed leaves extend beyond it (Fig. veloped by D. W. Bierhorst) were taken through 1, 2). The leaves exhibit considerable variation an ordinary dissecting microscope fitted with a in terms of size, number and shape of lobes, pres­ paper diaphragm for improved depth of field or ence or absence of fertile spikes, and number of with a Leitz Aristophot 4 x 5 view camera with fertile spikes borne by fertile leaves. When ma­ a 32-mm lens. Some of the gametophytes were ture, all leaves are pendant or arching, their subsequently dehydrated in a t-butanol series, laminar segments oriented approximately parallel embedded in Paraplast, and sectioned at 10-12 to the surface of the palmetto. microns by standard methods. Sections were Gametophytes of O. palmatum were found in stained with either safranin and fast green or large numbers at the locality. Although perhaps Sharman's (1943) tannic acid-iron alum-orange only a dozen palmettos bearing sporophytes were G-safranin. Other gametophytes were cleared in investigated for gametophytes, nearly two hun­ a mild clearing reagent developed by Herr (1971). dred complete gametophytes and several hundred The cleared gametophytes were examined and detached gametophyte apices were collected. photographed with a Zeiss compound microscope These were not, however, randomly distributed equipped with Nomarski interference-contrast among the palmettos. The amount of moisture optics. By focusing at various planes, it was pos­ present at the interface of the palmetto leaf-base sible to obtain a series of relatively undistorted mantle and the stem strongly influences gameto­ optical sections through portions of intact speci­ phyte distribution. Those palmettos with an es­ mens. This method was of little use, however, in sentially dry mantle and having an accumulation regions of high cytoplasmic density such as ga­ of dusty, loose debris, invariably lacked gameto­ metophyte apices. phytes. The best gametophyte growth was ob­ served on palms with tightly appressed frond bases OBSERVATIONS-Of the tree species present at which offered a relatively more moist and com­ the Collier County locality, only one, Sabal pal­ pact substratum. metto, is colonized by Ophioglossum palmatum. Attaining heights of 5 meters or more at this site, Gametophytes-The nongreen, mycotrophic ga­ the Cabbage Palmetto is characterized by a woody metophytes of O. palmatum are fundamentally mantle of persistent, imbricate leaf bases which cylindrical and much branched. However, they on most plants extends from the crown down to exhibit a considerable degree of variation in terms near ground level (Fig. 1). The decaying ma­ of overall form, cross-sectional shape, and size terials which accumulate within and underneath (Fig. 4, 6-23, 26, 28). Branches are most often the leaf-base mantle, providing the substratum oriented in several planes but may be confined to for the gametophytes and sporophytes of O. pal­ a single plane. In the latter case, the develop­ matum, appear to be derived primarily from the ment of stellate or nearly stellate forms can occur decay of leaf-base tissues. Fall litter is unlikely (Fig. 4). For descriptive purposes, many game­ to contribute significantly to the buildup of or­ tophytes may be regarded as comprising two dis­ ganic debris because of the tightly appressed na­ tinct regions: an expanded and sometimes flat­ ture of the palmetto leaf bases.