Spore Morphology and Systematics of the Genus Christensenia

Abstract

The spores of Christensenia are echinate, and superficially similar. How- ever, detailed SEM study reveals differences in spore shape, size, and exospore characters, such as spine distance, length, curvature, banding, apex morphology, and fusion. These differences are taxonomically significant and correlate completely with characters of gross morphology in the three taxa in the genus. In a recent revision, Rolleri (1993) segregated the genus Christensenia Max- on into the following taxa: C. aesculifolia Blume subsp. aesculifolia, C. aes- culifolia Blume subsp. korthalsii (de Vriese) Rolleri, and C. lobbiana (de Vriese) Rolleri. In that paper, spore morphology was considered to be unim- portant taxonomically, and spores were only described as monolete, elliptic in polar view, with a conical/spinulose ornamentation of close, short, sharp but soft spine-like processes (Rolleri, 1993, p. 14). Later observations of Christensenia spores, however, suggested that they var- ied more than previously thought. Therefore, we decided to study spores with a scanning electron microscope (SEM), especially to search for possible cor- relations with the morphological data presented by Rolleri (1993). This is the first analysis of specific and infraspecific variation within a genus of Marat- tiales, although spores of extant genera and species of the order have been studied and described for well over a century. Previous studies involving Christensenia considered it to be monotypic, and descriptions and illustrations of its spores were always attributed to C. aes- culifolia (Edrtmann and Sorsa, 1971; Morucchio, 1973; Devi, 1977; Hill and Camus, 1986; Tryon and Lugardon, 1990). Erdtman and Sorsa (1971) described apparently monolete perispores having an outer wall densely ornamented with spines. Morucchio (1973) described trilete, echinate spores and the possible presence of a perispore. Devi (1977, p. 99) described the spores as monolete and devoid of perine, with inconspicuous laesura. Hill and Camus (1986) stated that the spores may be trilete, or alete within a single syn- angium. They also described ornamentation as being prominently spinulose, with large spines, a feature of the sporoderm that they considered derived in