The identity of Isothecium marocanum Thér. & Meyl.

Abstract

Within a larger study of the genus Isothecium, a search for type material of Isothecium marocanum Ther. & Meyl. was performed. This taxon was described from Morocco in 1932 (Theriot & Meylan, 1932), but has not been further reported or revised. Type material was not found during a general search for all available Moroccan bryophyte material in Paris (PC; R. M. Ros and M. J. Cano, pers. comm.), where I. Theriot's original herbarium is located, but we traced an isotype in J. Braun-Blanquet's herbarium with the help of J. Mathez in Montpellier (MPU) and B. Toussaint in Bailleul (BAIL). Braun-Blanquet's bryophyte herbarium will soon be moved from BAIL to MPU, where the rest of his herbarium is already housed. The isotype is mixed with Homalothecium sericeum (Hedw.) Schimp., which was also noted on the envelope of the type, and a small piece of Orthotrichum lyellii Hook. & Taylor. Originally, Theriot had written an unpublished herbarium name on the specimen, but it undoubtedly belongs to the species we today call Scorpiurium deflexifolium (Solms) M.Fleisch. & Loeske. The type of I. marocanum agrees completely with the latter in leaf shape and areolation. The leaves are ovate, strongly narrowed towards their insertion, and gradually narrowed towards a broadly acute apex. The single costa ends shortly below the leaf apex, and the margin is recurved in its lower part and plane and denticulate or strongly so above. The marginal cells are similar to those further in, whereas in Isothecium the marginal cells are frequently shorter than the lamina cells closer to the costa. The median leaf lamina cells are 15-4065-9 mm and smooth, and the rectangular, quadrate or rhomboidal alar cells form a triangular or ovate, indistinctly delimited unistratose group that extends up along leaf margin 20-30% of the leaf length. In Isothecium the alar cells are usually partly bistratose near the leaf insertion, strongly incrassate, opaque and form indistinct, yellowish to brownish auricles. All the material of Isothecium marocanum is sterile, and sporophytes have not been described (Theriot & Meylan, 1932). While the holotype could potentially exist in Meylan's herbarium in Lausanne (LAU), we do not lectotypify the name, but make the following synonymy: