Diplazium delitescens and the Neotropical Species of Asplenium sect. Hymenasplenium

Abstract

Since the original description of Diplazium delitescens Maxon, no one has seriously questioned its generic disposition. However, a preliminary study of herbarium material of this uncommon neotropical species suggests that it might be better placed in Asplenium. Maxon relied chiefly on the back-to-back arrangement of linear sori in ascribing this species to Diplazium. In contrast, spleenworts generally have only single, linear sori on the ultimate veins. Although soral arrangement is the primary (and usually most reliable) character used to separate the two genera, I report here a survey of additional characters that provide good evidence for transferring D. delitescens to Asplenium. Sporangia.-The species of Asplenium consistently have one-rowed sporangial stalks, at least at the base (Bower, 1928, p. 140; Tardieu-Blot, 1932, p. 363) and sporangial capsules that often split divaricately at the tip of the fully extended or backwardly flexed annulus. Diplazium delitescens possesses both these characteristics (Fig. 1). Other species of Diplazium have shorter, twoor three-rowed sporangial stalks, with annuli often not extended and capsules not splitting divaricately at the tip, e.g., D. werckleanum Christ (Fig. 2). I have been unable to find any reference to this distinctive type of sporangial opening in Asplenium, but I believe it may be a very useful character in distinguishing asplenioid species from other groups of ferns. The number of annular cells inAsplenium is generally higher than in Diplazium. Tardieu-Blot (1932, p. 364) reported 15-20 annular cells for species of Diplazium and 20-25 annular cells for species of Asplenium. Copeland (1947, p. 147) listed Diplazium (inAthyrium) as having an of 12-20 (commonly 16) thickened cells, whereas Asplenium was described as having an usually of 20-28 cells. I have made five counts each onA. laetum Swartz (Breedlove 33893, DS), A. abscissum Willd. (Breedlove 22178, DS), A. harpeodes Kunze (Breedlove 22504, DS), and A. auriculatum Swartz (Breedlove 22506, DS); these species averaged 23, 20, 21, and 20 annulus cells per sporangium, respectively. Diplazium franconis Liebm. (Breedlove 22421, DS), D. lonchophyllum Kunze (Breedlove 22461, DS), D. acutale Fee (Breedlove 22760, DS), and D. werckleanum Christ (Breedlove 33664, DS) all averaged 15 annular cells per sporangium. Diplazium delitescens (Breedlove 33853, DS) averaged 21 annular cells per sporangium, which agrees with Asplenium. Spores.-Diplazium delitescens spores have numerous, sharp folds in the perispore (Fig. 3), and are similar to, or even indistinguishable from, spores of several species of Asplenium from southern Mexico and Central America, e.g., A.