Chapman's Quillwort Reconsidered

Abstract

Certainly one of the least known pteridophytes in the southeastern United States is Chapman's Quillwort. Described by Engelmann (1882) as Isoetes flaccida Shuttlew. var. chapmanii Engelm., the taxon has been collected only a few times since its initial collection by A. W. Chapman in 1848. The collections are always from the same general locality in Jackson County, Florida. Larger megaspores with smoother ornamentation were said by Engelmann to distinguish it from the typical variety. Underwood (1900) and Clute (1928) both recognized the distinctness of the taxon, and Small (1932) even elevated it to specific status. Lakela and Long (1976) maintained I. chapmanii (Engelm.) Small, and in their key distinguished it from I. flaccida on the basis of megaspore ornamentation and sporangium shape. On the other hand, Pfeiffer (1922) and Boom (1979, 1982) were not convinced of the distinctness of I. chapmanii, and they synonymized it with I. flaccida. Recently I was able to study the spores of these plants more carefully by means of scanning electron microscopy (SEM), and I now regard the evidence as sufficient for maintaining I. flaccida var. chapmanii as a rare, but distinct element of Florida's pteridophyte flora. Spores were coated by a two-step procedure consisting of the deposition from a low voltage arc of an initial carbon layer onto which was subsequently sputtered a 60:40 gold-palladium alloy using a 15 watt DC diode coater. Specimens were examined with a Cambridge S4-10 SEM. Photographs were taken with Polaroid Type 665 Positive/Negative Land Film. Spores of some thirty specimens of Isoetes flaccida were examined (vouchers cited in Boom, 1979), but the photomicrographs of only three are presented herein: var. flaccida: Lake Flirt, near Lake Okeechobee, Florida, Aug 1878, A. P. Garber s. n. (US 240797); cypress pond near Cobb, Sumter Co., Georgia, R. M. Harper 1046 (US 400120); and var. chapmanii: Tributary of the Chipola River at Marianna, Jackson Co., Florida, R. K. Godfrey 61963 (US 2424571). Both megaspores and microspores of the two varieties show differences in perine ornamentation which are taxonomically significant (Figs. 1-6). Additionally, the differences in megaspore size provide a useful means of distinguishing the varieties. The ornamentation of I. flaccida var. chapmanii megaspores is low tuberculate, densely so on the distal hemisphere and sparsely so on the proximal (Fig. 1). Greater magnification shows the perine to be minutely echinate (Fig. 3). In var. flaccida, the megaspores are also low tuberculate, but densely so on both hemispheres (Fig. 2). Greater magnification reveals a finely rugulate perine, the muri anastomosing so as to give a spongy appearance (Fig. 4). The diagnostic perine characters (extent and distribution of tubercules) can be seen at 40X, and the size difference detected with a dissecting microscope. Although the microspores of the varieties are essentially the same size, their perine ornamentation differs: that of var. chapmanii being echinate with an arach-