Selaginella nanophylla 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 : 239-242

Selaginella nanophylla Valdespino, C. López & L. Góes , sp. nov. ( Figs. 3 , 4 A–C )

Selaginella nanophylla differs from its relatives, S. epipubens Caluff & Shelton (2009: 116) and S. plagiochila Baker (1883: 212) , by its glabrous leaves surfaces (vs. hispid) and median leaves with entire to shortly dentate margins (vs. ciliate) and apiculate to cuspidate (0.03–0.1 mm) apices (vs. long-aristate, 0.2–0.3 mm in S. epipubens and 0.3–0.5 mm in S. plagiochila ).

Type: — CUBA. Holguín: Vicinity of Camp San Benito, Oriente , 900 m, 24 February 1910, J . Shafer 4096 (holotype NY!, isotype PMA!) .

Plants terrestrial or epipetric. Stems prostrate, stramineous, 4–10 mm long, 0.2–0.4 mm diam., inarticulate, not flagelliform or stoloniferous, 1 or 2-branched. Rhizophores axillary, borne throughout stem, filiform, 0.1 mm diam. Leaves dimorphic throughout, coriaceous. Lateral leaves distant, spreading or slightly ascending apically, broadly ovate to ovate-elliptic, 0.7–1.0 × 0.4–0.7 mm; base rounded or truncate, acroscopic base overlapping the stem, basiscopic base free from the stem, margins slightly to obscurely hyaline, 1 or 2 cells wide, the cells elongate and papillate, parallel to margin, papillae in 1 or 2 rows over cell lumen, entire or shortly ciliate (0.05–0.1 mm) to dentate apically; apex apiculate to cuspidate (0.03–0.10 mm), may end in two divergent cilia, recurved or acute if tips broken off; both surfaces glabrous, upper surface made up of rounded to quadrangular, sinuate-walled cells, many of them papillate, papillae 4–14 over cell lumen, without stomata or idioblasts, lower surface made up of elongated to rectangular, straight to sinuate-walled cells, with many stomata and obscure, papillate, idioblast-like cells. Median leaves distant, ascending, ovate to ovate-deltate, 0.3–0.4 × 0.2–0.3 mm; base oblique or truncate, inner base plane, outer base ventricose; margins hyaline, 2 or 3 cells wide, the cells elongate and papillate parallel to margin, papillae in 1 or 2 rows over cell lumen, entire or shortly dentate apically; apex apiculate to cuspidate (0.03–0.10 mm), may end in two divergent cilia, recurved or acute if tips broken off; both surfaces glabrous with stomata, upper surface made up of quadrangular to rounded, sinuate-walled cells, many of them papillate, papillae 4–14 over cell lumen, without idioblasts, lower surface made up of elongated to rectangular, straight to sinuate-walled cells, with obscure, papillate, idioblast-like cells. Axillary leaves similar to lateral leaves. Strobili terminal on branch tips, one per branch, compact or loose when mature, usually quadrangular, 0.5–4 mm long. Sporophylls monomorphic, without a laminar flap, ovate, 1.0–1.2 × 0.5–0.7 mm, with a slightly developed keel apically along midrib on upper surface; base rounded; margins hyaline, entire or denticulate; apex apiculate (0.05–0.10 mm) with a recurved tip; both surfaces glabrous with obscure, papillate 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 hyaline to slightly greenish-hyaline. Megasporangia one or two apically in ventral rows; megaspore white, proximal and distal faces rugose with scabrate microstructure, 270–275 µm diam. Microsporangia in dorsal and ventral rows; microspores deep orange, proximal face rugose, distal face pilate to baculate, 24–31 µm diam.

Habitat and Distribution: — Cuba; terrestrial or epipetric, on serpentine at 200–900 m.

Etymology: — The specific epithet is derived from the Greek, nano, dwarf, and phyllus, leaf; referring to the extremely small leaves of this species.

Conservation Status: — There is still insufficient data to ascertain the complete distributional range, abundance and possible threats to this species, therefore, only a conservation assessment of Data Deficient (DD), following IUCN categories and criteria ( IUCN 2012) is made at this time.

Additional Specimens Examined (Paratypes): — CUBA. Guantánamo: Baracoa, orillas del Arroyo Blanco ,

camino a Vega de La Palma, 26 February 1979, González 40060 (HAJB). Holguín: Moa, La Veguita, La Breña, 200–300 m, 13 April 1981, Bisse et al. 40062 (HAJB), October 1989, Pochs 456 (PMA), Río Jaragua, Minas de Cayoguán, Punta Gorda, July 1945, Clement 4643 ( US), Río Yagrumajes, 14 April 1945, Acuña 12360 (US-2 sheets), Sierra de Nipe, Río Piloto, ca. 700 m, 21 September 1922, Ekman 15172 (NY). Santiago de Cuba: Segundo Frente, Cima del Pico Cristal, 30 April 1985, Álvarez et al. 57181 (HAJB).

Discussion:— Selaginella nanophylla is one of the smallest plants and has the smallest leaves in the genus. It is easily overlooked by collectors, and may be more widely distributed than recorded. It grows on serpentine soil in the mountains of eastern Cuba, a recognized center of speciation and endemism ( Borhidi 1991, Fa et al. 2002, Majure et al. 2014). According to Majure et al. (2014), the region including Sierra de Moa, Nipe Mountains and Sierra de Cristal (where S. nanophylla grows), is made up of serpentine bedrock and has the highest number of endemics in Cuba, which has about one-third of its endemic flora on this type of soil ( Borhidi 1991). This suggests that S. nanophylla is probably a local endemic to this region.

Selaginella nanophylla is distinguished from other small-leaved Cuban Selaginella by having the upper surface of median leaves with few (2 or 3) stomata that are restricted to the medial and submedial regions ( Fig. 3B ) but on the lower surface has (3–6), particularly at the outer base region ( Fig. 3C & D ), whereas in the case of the lower surface of lateral leaves it has many stomata that are primarily medial and supramedial and some perimedial near the apex ( Fig. 3C & D ). Furthermore, this species is characterized by having the upper surface of lateral and median leaves made up of roundish to quadrangular, papillate or non-papillate cells ( Fig. 3A & B ). Additionally, S. nanophylla is characterized by having obscure idioblast-like cells on the lower surface of median and lateral leaves and on the upper surface of sporophylls (when viewed with a stereoscope) that are conspicuously papillate when observed on SEM ( Figs. 3C & D ; 4A–C ).

In one of the studied specimens, Ekman 15172 (NY), the apiculate to cuspidate apices of the lateral and median leaves are tipped by one or two cilia.

Selaginella nanophylla can be confused with S. epipubens and S. plagiochila because of its prostrate stems, small leaves, broadly ovate to ovate-elliptic lateral leaves, and rhizophores borne throughout the stems. It can be separated from those species by the characters given in the diagnosis. Additionally, S. nanophylla has glabrous sporophylls (vs. hispid at least along midrib) with entire or denticulate margins (vs. ciliate) and apiculate apices (vs. acuminate to aristate) ( Fig. 4 ), and lateral leaves with apiculate to cuspidate apices (vs. acute to slightly rounded in S. plagiochila or rounded to acute in S. epipubens ). It differs further from S. plagiochila by lateral leaves with margins entire or shortly ciliate (0.05–0.1 mm) to dentate apically (vs. long ciliate, 0.3–0.4 mm) and from S. epipubens by median leaves upper surface with 2 or 3 stomata (vs. 15–20), which are restricted to the medial and submedial regions (vs. perimedial and marginal).

Figures

FIGURE 3. SEM micrographs of stem and leaves of Selaginella nanophylla (Shafer 4096, NY).A. Upper surface of stem. B. Upper surface of median and lateral leaves showing papillate cells and stomata distribution on median leaves. C. Lower surface of stem showing stomata distribution on lateral and median leaves. D. Lower surface of lateral and median leaves showing stomata distribution and submarginal, papillate idioblast-like cells.

FIGURE 4. SEM micrographs of strobili and sporophylls. A–C. Selaginella nanophylla (Clement 4643, US). A. Ventral side of mature strobilus. B. Upper surface of ventral sporophyll showing entire margins (a), papillate, idioblast-like cells (b), and stomata (c). C. Upper surface of dorsal sporophyll showing very small teeth on margins (a), papillate, idioblast-like cells (b), stomata (c), rounded to quadrangular, sinuate-walled cells (d), and elongate, sinuate-walled cells on lamina half that overlaps with ventral sporophyll (e). D–E. S. epipubens (Britton et al. 14418, NY). D. Ventral side of mature strobilus showing ciliate sporophylls with ciliate keel. E. Ventral sporophylls showing marginal cilia (a), stiff hairs along keel (b), and papillate idioblasts (c). F–G. S.plagiochila (Wright 942, isotype NY).F. Dorsal side of mature strobilus. G. Dorsal sporophyll showing marginal cilia (a), stiff hairs along keel (b), stiff hairs on lamina surface (c), and stomata (d).