Selaginella myriostachya Valdespino, C. López & L. Góes, 2014

Valdespino, Iván A., López, Christian & De Araújo Góes-Neto, Luiz A., 2014, Additions to Cuban Selaginella (Selaginellaceae), Phytotaxa 184 (4), pp. 235-244 : 236-239

Selaginella myriostachya Valdespino, C. López & L. Góes , sp. nov. ( Figs. 1 & 2 )

Selaginella myriostachya differs from S. flabellum (Desvaux ex Poiret 1814: 558) Spring (1843: 234) by its very slightly dimorphic (vs. obviously dimorphic) leaves below the first branch of the stem, ovate-oblong or lanceolate-oblong lateral leaves (vs. narrowly ovate) that are short-ciliate (0.05–0.1 mm) along basal ¼ of acroscopic margin (vs. long-ciliate, 0.2–0.5 mm, along basal ½), and lanceolate or ovate-elliptic median leaves (vs. narrowly lanceolate) with a weekly developed outer auricle attached to the stem (vs. well-developed and free from the stem).

Type:— CUBA. Pinar del Río: Viñales, Parque Nacional Viñales, Cueva de Santo Tomás , 6 July 2013, I. Valdespino et al. 2013-1 (holotype PMA!, isotypes B!, HAJB!, K!, NY!, UC!) .

Plants epipetric. Stems suberect to erect, pale-green, 5–20 cm long, 0.8–1 mm diam., inarticulate, not flagelliform or stoloniferous, 2 or 3-branched. Rhizophores ventral, restricted to the base, filiform, 0.1–0.3 mm diam. Leaves at stem base very slightly dimorphic (seemingly monomorphic), obviously dimorphic shortly below first branch and throughout the rest of stem, membranaceous. Lateral leaves distant, spreading to ascending, ovate-oblong or lanceolate-oblong, 1.8–2.2 × 0.8–1.0 mm; base rounded to slightly truncate, acroscopic base overlapping the stem, basiscopic base free from the stem; margins hyaline, 2 or 3 cells wide, the cells elongate and papillate parallel to margin, papillae in a single row over cell lumen, short-ciliate (0.05–0.10 mm) along basal ¼, otherwise serrate apically; apex cuspidate (0.05–0.10 mm) or acute if tips broken off; both surfaces glabrous, upper surface made up of rounded to quadrangular, sinuatewalled cells, without stomata or idioblasts, lower surface made up of elongated, sinuate-walled cells, with stomata along central portion of midrib and with obscure, papillate idioblasts. Median leaves distant to slightly imbricate apically, ascending, lanceolate or ovate-elliptic, 0.8–1.3 × 0.6–1.1 mm; base oblique, inner base truncate, outer base slightly auriculate, auricle attached to stem; margins narrowly hyaline made up of a band 1–3 cells wide, the cells elongate and papillate parallel to margin, papillae in a single row over cell lumen, short-ciliate (0.1–0.2 mm) along basal ¼, otherwise apically serrate; apex acuminate to short-aristate (0.1–0.4 mm); both surfaces glabrous without idioblasts, upper surface made up of rounded to quadrangular, sinuate-walled cells, some papillate, papillae 3–7 over cell lumen, with stomata along midrib, lower surface made up of elongated, sinuate-walled cells, without stomata. Axillary leaves similar to lateral leaves. Strobili terminal on branch tips, one per branch, loosely quadrangular, 1.5–5 mm long. Sporophylls monomorphic, without a laminar flap, ovate, 1.0–1.2 × 0.5–0.6 mm, with a slightly developed keel apically along midrib on upper surface; base rounded; margins hyaline, dentate; apex acuminate (0.05–0.10 mm); both surfaces with idioblasts; dorsal sporophylls with upper surface green, except for the half that is overlapping the ventral sporophylls where it is hyaline, lower surface greenish-hyaline; ventral sporophylls with both surfaces greenish-hyaline. Megasporangia along basal half of ventral rows; megaspores deep orange, proximal and distal faces rugose-reticulate with echinate microstructure, 340–357 µm diam. Microsporangia in dorsal rows and apically in ventral rows; microspores deep orange, proximal face rugose, distal face baculate, 30–40 µm diam.

Habitat and Distribution:— Cuba; growing in patches on limestone rocks in caves with open ceiling and high humidity; ca. 400 m.

Etymology: — The specific epithet derives from the Greek myrio, countless, and stachyus, relating to a spike; referring to the many strobili on fertile plants.

Conservation Status: — Although this species is to be expected on or around Mogotes along Sierra de los Órganos in Pinar del Río province in western Cuba, it has a limited range of known distribution. It is found in localized populations that may be threatened by agriculture expansion and ecotourism activities such as caving. According to IUCN (2012) categories and criteria, it may be tentatively considered vulnerable ( VU) .

Additional Specimens Examined (Paratypes): — CUBA. Pinar del Río : Loma Harenales [Arenales], S of Sumidero, 20 August 1912, Shafer 13794 (F-2 sheets, GH, NY, UC, US); Lavadero to La Guira, N of Sumidero, 26 August 1912, Shafer 13845 ( BM, NY); Baños de San Vicente , 12–16 September 1910, Britton et al. 7341a ( NY); Cuba Orientali [Pinar del Río], Viñales , 1859–1860, Wright 1823 ( B, BM, GH, K-2 sheets, MO, P, US, W); 1924, Chrysler 15a ( US) .

Discussion: — Selaginella myriostachya is characterized by its suberect to erect stems covered by very slightly dimorphic, appressed leaves below the first branch ( Fig. 1 ) and oblique bases of median leaves, with a weekly developed outer auricle attached to the stem ( Fig. 2B ). Interestingly, below the first branch of the stem, the cell pattern on the upper surface of median and the lower surface of lateral leaves varies slightly than that on leaves above this section. In this region, the upper surface of median leaves is made up of more conspicuously quadrangular cells, most of which are covered by 4–11 papillae ( Fig. 1C–E ), whereas the lower surface of lateral leaves is made up of elongate, straightwalled cells, many of which are covered by 7–18 papillae ( Fig. 1G & H ). In addition, above the first branch of the stem the lower surface of lateral leaves have obscure idioblasts when observed with a stereoscope, which are conspicuous and obviously papillate as observed on SEM ( Fig. 2D ).

Selaginella myriostachya may be confused with the morphologically similar S. flabellum but differs from it by characters provided in the diagnosis and by having lateral leaves on branches that are mostly ascending (vs. spreading, giving a pectinate appearance to branches in S. flabellum ). In addition, S. myriostachya grows on limestone rocks associated with caves in Mogotes, which are habitats of high endemism in Cuba ( Rivera et al. 2008), particularly those around the Viñales Valley of Pinar del Río province in the western part of the island. Selaginella flabellum , previously known only from the Dominican Republic and Haiti ( Alston 1952), is recorded in eastern Cuba from the provinces of Holguín (e.g., Morton & Acuña 3300, US!; Ekman 2229, B!) and Santiago de Cuba (e.g., Clement 6671, US!; Garcia 51652, HAJB!; Roy & Acuña 8172, US!). These plants grow on wet soil stream banks.

Figures

FIGURE 1. SEM micrographs of stem section and leaves below first branch of Selaginella myriostachya (Valdespino et al. 2013-1, PMA). A. Stem section showing appressed, slightly dimorphic median (m) and lateral (l) leaves. B. Close up of A. C. Upper surface of median leaf. D. Close up of apical region of median leaf upper surface. E. Close up of basal region of median leaf upper surface. F. Stem section showing appressed lateral leaves. G. Lower surface of lateral leaf. H. Close up of mid region of lateral leaf lower surface.

FIGURE 2. SEM micrographs of stem and leaves of Selaginella myriostachya (Shafer 13794, NY). A. Upper surface of stem. B. Upper surface of median leaf. C. Lower surface of stem. D. Lower surface of lateral leaf.