Spore Morphology of Botrychium lunarioides

Abstract

Spore morphology was examined in the rare fern Botrychium lunarioides with the scanning electron microscope. Surface topography of the spore walls confirms the placement of B. lunarioides in the subgenus Sceptridium. Botrychium is a widespread genus of eusporangiate ferns classified within the family Ophioglossaceae. Clausen (1938) originally divided this genus into three subgenera based on vernation, dissection of the leaf blade, and gameto- phyte shape. Presently, four subgenera are recognized (Tryon and Tryon, 1982; Tryon and Lugardon, 1991): Botrychium, Japanobotrychium, Osmundopteris, and Sceptridium. Although some investigators (Kato, 1987 and discussion therein; Sahashi, 1976) have raised these subgenera to generic level, Wagner (1990) considered it best to retain the more conservative classification, at least for the present. Of particular use in placement of species within the proper subgenus has been spore morphology, in particular surface topography (Tryon and Lugardon, 1991). The scanning electron microscope (SEM) has proven a particularly use- ful tool for such studies. Botrychium lunarioides (Michx.) Sw. is a species restricted to the south- eastern United States. According to Warren H. Wagner (pers. comm.), is one of the rarest ferns in the United States, and not one botanist in a thousand has seen it. However, Watkins (1992) recently completed a status survey of this species in Alabama and while doing so discovered a number of new lo- calities. Also, Do et al. (1996) have shown this species to be more common in eastern Texas than previously thought. The species is considered to belong within the subgenus Sceptridium (Wagner and Wagner, 1993). Wagner (1992) gave an analysis of the distinctive features of B. lunarioides that differentiated it from other members of subgenus Sceptridium, and he placed it in a separate section, Hiemobotrychium. Thus, in spite of its distinctive characters, B. lu- narioides was still considered to belong to subgenus Sceptridium. However, no confirmatory evidence from spore morphology has been available. The pur- pose of this study is to provide that information. A recent study (Skoda, 1997) recommended placing B. lunarioides in a new monotypic genus as Holubiella lunarioides (Michx.) Skoda, based on a number of morphological features including tracheidal idioblasts in the leaf stalks. It remains to be seen how this proposal will be received by other pteridologists. For the purposes of the present manuscript, we shall follow the commonly