Selaginella brachyclada Baker

Figs 1, 2

Selaginella brachyclada Baker, Fern Allies: 45. 1887 [publ. May. 1887] ≡ Selaginella diminutifolia Jenman, Gard. Chron., ser. 3. 2: 99. 1887 [pub. 23 Jul. 1887]. Type: Guyana. Essequibo, [Potaro River], foot of the Kaieteur, [5°13'N, 59°25'W], [Sep. – Oct. 1881], G. S. Jenman 1481 (holotype: K! [K 000589210]; isotypes: BM! [BM 000905721], NY!).

Description.

Plants terrestrial or epipetric. Stems creeping, stramineous, 3–20 cm long, 0.2–0.6 mm diam., non-articulate, not flagelliform or stoloniferous, 2–3 - branched, these often flagelliform. Rhizophores ventral, borne throughout the stem length, filiform, 0.1–0.3 mm diam. Leaves chartaceous or coriaceous, heteromorphic, of three types (ventral, median, and axillary). Lateral leaves distant, ascending and spreading at 60 ° to the stems, ovate-deltate on main stems or narrowly ovate to ovate, or ovate-oblong on distal portions of the main stems and branches, 1.3–2.5 × 1.0– 1.9 mm; bases subcordate on main stems or rounded on distal portions of main stems and branches, glabrous, the acroscopic bases strongly overlapping stems, the basiscopic bases free from the stems; acroscopic and basiscopic margins greenish, continuously bordered by quadrangular cells, sparsely denticulate or entire throughout, the acroscopic and basiscopic margins on the lower surfaces hyaline or greenish hyaline, bordered by a band 1–5 cells wide of elongate, straight-walled and papillate idioblasts, the papillae 4–12 in one row in each cell lumen; apices acute to broadly acute, tipped by 2–5, short, tooth-like hairs; upper surfaces glabrous, except for submarginal tooth-like hairs along the basiscopic margins, comprising rounded to quadrangular, irregularly, sinuate-walled and papillate cells, the papillae 2–6 on each cell lumen, with stomata along the basiscopic margins, and with submarginal tooth-like hairs, the lower surfaces comprising elongate, sinuate-walled, and laevigate cells and with some, sparsely distributed, elongate, sinuate-walled, and papillate idioblasts, the papillae 15–35 arranged in two rows on each cell lumen, with stomata in 1–3 rows along midribs and on 1 row along basiscopic margins, the midribs stramineous and plane on side view. Median leaves distant, ascending and overlapping the stems, ovate to broadly ovate, or ovate-deltate to cordate, 0.8–1.5 × 0.5–1.2 mm, bases glabrous, rounded or subcordate, without auricles; the inner margins on both surfaces hyaline, continuously bordered by a narrow band of idioblasts, the band 1–3 cells wide, the idioblasts as in the lateral leaves, denticulate or entire, the outer margins on both surfaces greenish, comprised of quadrangular cells along proximal 1 / 2, and distally as in the inner margins; apices broadly acute or shortly attenuate, each usually tipped by 1–4 tooth-like, stiff, short hairs or this caducous; the upper surfaces glabrous, comprised of quadrangular to rounded, papillate cells, the papillae 4–6 on each cells lumen, without idioblasts, with the midribs prominently raised on side view along distal 1 / 2 – 3 / 4 where stomata are found in 1–4 rows and submarginally on the outer margins, the lower surfaces as in the lateral leaves. Axillary leaves ovate-deltate to subcordate or ovate-lanceolate, 1.2–2.5 × 0.8–1.8 mm; bases subcordate to rounded; margins, apices, and leaf surfaces as in the lateral leaves. Strobili terminal on the branch tips, laxly quadrangular to flattened and dorsiventral, 10–15 mm. Sporophylls monomorphic, ascending, imbricate, keeled along the midribs, the keels distally puberulent with short, teeth-like projections on the upper surfaces, without laminar flaps, ovate, 0.8–1.0 × 0.5–0.8 mm; bases rounded to rounded-oblique; apices acute to shortly-attenuate, 0.05–0.1 mm long; stomata found along the midribs; dorsal sporophylls with the inner margins hyaline, bordered by 1–3 rows of elongate, straight-walled and papillate idioblasts similar to those of the median leaf margins, without marginal stomata, entire on proximal 1 / 2 – 2 / 3, otherwise sparsely denticulate distally, the outer margins greenish, bordered by rounded to quadrangular cells and with marginal stomata along proximal 1 / 2, entire along proximal 1 / 2, otherwise sparsely denticulate distally; the upper and lower surfaces of the leaf laminae as in the median leaf surfaces; ventral sporophylls margins hyaline, bordered by 1–3 rows of elongate, straight-walled and papillate idioblasts, entire on proximal 1 / 4 and sparsely denticulate along distal 3 / 4, without marginal stomata; apices as in the dorsal sporophylls; the upper and lower surfaces of the leaf laminae hyaline to greenish-hyaline, composed of elongate, straight-walled, and laevigate cells. Megasporangia in two ventral rows; megaspores light yellow to cream, with a prominent equatorial flange, proximal faces rugulate to rugulate-reticulate, distal faces reticulate, the microstructure of proximal and distal faces not observed, 350–400 µm diam. Microsporangia in two dorsal rows; microspores orange, proximal and distal faces laevigate, micro-ornamentation not observed, 25–48 µm diam.

Habitat and distribution.

Selaginella brachyclada typically grows on moist rock ledges and seepage surfaces near waterfalls in tropical savanna and along gallery and riparian forests. It is known from Guyana (the type locality) and, in Venezuela, it occurs at mid-elevations (995–1200 m) in the Gran Sabana region (Guayanan savanna ecoregion), Bolívar State, southeastern Venezuela. Due to the continuity of suitable habitats, the species is likely to occur in neighboring Roraima, in northern Brazil, although this has not yet been confirmed.

Conservation status.

Selaginella brachyclada is known from only six collections: the type, collected at the base of Kaieteur Falls in Kaieteur National Park (Guyana), and five collections from the Gran Sabana region within Canaima National Park (Bolívar State, Venezuela). Using GeoCAT with the IUCN-recommended 2 - km grid, these records yield an extent of occurrence (EOO) of 4,128.942 km 2 and an area of occupancy (AOO) of 20 km 2. Although Selaginella brachyclada is known from protected areas (e. g., Canaima National Park in Venezuela), portions of the Gran Sabana sector are affected by frequent, human-ignited fires linked to local land-use practices such as shifting cultivation and hunting (Bilbao et al. 2010). Changes in fire use have been associated with forest and habitat loss, and fire is considered a major threat because it may promote forest substitution by treeless savannas in the savanna – forest mosaic of the Gran Sabana (Bilbao et al. 2010). In addition, gold mining within Canaima National Park has been documented as largely informal and illegal, often conducted without permits, supporting its classification as an ongoing pressure that can drive local habitat disturbance and degradation (García Bonet 2020). The species is therefore assessed as Endangered under IUCN Criterion B (EN B 1 ab (iii) + B 2 ab (iii)) following IUCN Standards and Petitions Committee (2022).

Specimens examined.

Venezuela • Bolívar: 75 km N of Santa Elena de Uairén and 232 km S of El Dorado, 5°15'N, 61°15'W, alt. 1200 m, 19 Dec. 1978, J. A. Steyermark & V. Carreño E. 117881 (GH, VEN), J. A. Steyermark & V. Carreño E. 117886 (GH, VEN); • Gran Sabana, near Salto del Aponguao, 42.5 km NE of Misión of Santa Teresita de Kavanayén, alt. 1130 m, 22 Feb. 1978, J. A. Steyermark et al. 115575 (BM, GH, VEN), J. A. Steyermark et al. 115583 (BM, GH, VEN); • Kama-Merú, alt. 995 m, 6 Apr. 1988, V. Marcano, C. Sastre, F. Sastre & S. Hernández 999 (mixed coll. 999 a at P, VEN).

Discussion.

Selaginella brachyclada is characterized by its ovate to broadly ovate, or ovate-deltate to cordate median leaves with rounded to subcordate bases, with the inner margins hyaline and denticulate or entire, the apices broadly acute or shortly attenuate, each usually tipped by 1–4 stiff, tooth-like, short hairs or these caducous, with the midribs prominently raised on side view along distal 1 / 2 – 3 / 4 where stomata are arranged in 1–4 rows and submarginally on the outer margins. Additionally, S. brachyclada has distinctly ovate-deltate to subcordate or ovate-lanceolate axillary leaves with subcordate to rounded bases and denticulate margins.

As noted earlier, Selaginella brachyclada was historically misidentified as S. porelloides and was later synonymized with S. rhodostachya. It is distinguished from S. porelloides by its ovate-deltate (vs. semicordiform to cordiform) lateral leaves with acroscopic margins greenish (vs. hyaline), denticulate (vs. serrate to shortly ciliate along proximal 1 / 2, serrulate to entire distally), and median leaves with rounded to subcordate (vs. cordate to subcordate) bases, lacking (vs. with two slightly developed or less frequently lacking) auricles, broadly acute or shortly attenuate (vs. short- to long-acuminate or less frequently short-aristate) apices, the tip less that 1 / 8 (vs. acumen or arista 1 / 4 or less) the length of laminae, each 0.1 mm or less (vs. 0.3–0.6 mm) long. Additionally, the median leaf upper surfaces have raised (vs. plane) midribs with inconspicuous stomata along the distal 1 / 2 – 3 / 4 and submarginally on the outer margins (vs. with conspicuous stomata scattered throughout the leaf laminae).

Selaginella brachyclada differs from typical S. rhodostachya (i. e., those specimens with caducous, leaf marginal hairs) by its ovate to broadly ovate or ovate-deltate to cordate (vs. ovate-elliptic) median leaves, usually tipped by 1–4 tooth-like, stiff, and short (vs. two, divergent, long) hairs, and ovate-deltate (vs. narrowly-elliptic or elliptic-ovate) lateral leaves. It’s lateral leaves with subcordate (vs. rounded) bases on the main stems, and ovate-deltate to subcordate or ovate-lanceolate (narrowly elliptic) axillary leaves. Selaginella brachyclada is even more clearly distinguished from the form of S. rhodostachya formerly assigned to S. valdepilosa Baker subsp. tricholoma by its sparsely denticulate (vs. long-ciliate) leaf margins.

Selaginella brachyclada may be confused with S. muscosa Spring, from which it differs by its coriaceous (vs. papyraceous) leaves, denticulate (vs. shortly ciliate along basal 3 / 4, otherwise serrate to serrulate along distal 1 / 4) median leaf margins with acute to short-acuminate (vs. short to long-acuminate or long-aristate) apices, and by lacking (vs. with conspicuous) idioblasts on the upper leaf surfaces.