Selaginella stomatoloma Valdespino, 2015

Valdespino, Ivan A., 2015, Novelties in Selaginella (Selaginellaceae - Lycopodiophyta), with emphasis on Brazilian species, PhytoKeys 57, pp. 93-133 : 100-103

Selaginella stomatoloma Valdespino sp. nov. Figure 10

Diagnosis.

Selaginella stomatoloma differs from the recently described Selaginella saltuicola Valdespino by having the upper surfaces of the leaves with glabrous (vs. papillate) cells, the lateral leaf lower surfaces without (vs. with) papillate idioblasts and with marginal cells glabrous (vs. papillate), and acute (vs. rounded to broadly acute) apices, the median leaf margins comprising slightly elongate and glabrous (vs. strongly elongate and papillate) cells, these denticulate (vs. entire), with short-acuminate (vs. acute) apices, and upper surfaces with few submedial and submarginal stomata (vs. stomata throughout laminae).

Type.

BRAZIL. Pará: Canaã dos Carajás, S11D, UTM-Zone 22M: 9293819 575625 [06°23'08"S, 50°18'58.24"W], 31 Aug 2010, T.E. Almeida et al. 2518 (holotype: PMA! [PMA103369]; isotype: BHCB [BHCB142524]-n.v.).

Description.

Plants epipetric. Stems decumbent to ascending, stramineous, 3-6 cm long, 0.2-0.5 mm diam., non-articulate, not flagelliform, stoloniferous, 1- or 2-branched. Rhizophores axillary, borne on proximal ¼-¾ of stems, filiform, 0.05 or 0.15 mm diam. Leaves heteromorphic throughout, membranaceous, both surfaces glabrous, upper surfaces green, lower surfaces silvery green. Lateral leaves spreading to ascending near branches and stem apices, ovate-elliptic to ovate-oblong, 1.5-2.0 × 0.8-0.9 mm; bases rounded, acroscopic bases slightly overlapping stems, basiscopic bases free from stems; margins greenish with the cells quadrangular, sinuate-walled, glabrous, mostly entire and denticulate near apices or denticulate throughout; apices acute and variously tipped by 1 or 2 teeth; both surfaces without idioblasts, upper surfaces comprising quadrangular to rounded, sinuate-walled, glabrous cells, with stomata submarginal, particularly on distal ½ and throughout margins, lower surfaces comprising elongate, sinuate-walled, glabrous cells, with stomata in 3-5 rows along midribs and throughout acroscopic halves of the laminae. Median leaves distant or imbricate near branches and stem apices, ascending, ovate-elliptic or elliptic, 0.7-1.1 × 0.3-0.6 mm; bases rounded to slightly oblique; margins greenish or narrowly hyaline in a band 2 or 3 cells wide, the cells slightly elongate, straight-walled and glabrous parallel to margins, denticulate throughout; apices short-acuminate, each acumen 0.05-1.05 mm, denticulate on upper surfaces, tipped by 1 or 2 teeth; both surfaces without idioblasts, upper surfaces comprising quadrangular to rounded, sinuate-walled, glabrous cells, with stomata in 1-3 rows along midribs, with a few submedial and submarginal and throughout margins, lower surfaces comprising elongate, sinuate-walled cells, without stomata. Axillary leaves similar to lateral leaves. Strobili terminal on branch tips, quadrangular, 1.5-6.0 mm. Sporophylls monomorphic, without a laminar flap, each with a strongly developed and seemingly entire or denticulate keel along midribs, ovate or the ventral ones broadly ovate, 0.9-1.2 × 0.4-0.7 mm; bases rounded; margins narrowly hyaline (less so on ventral sporophylls), denticulate; apices acute to short-acuminate, each acumen 0.05-0.1 mm with margins dentate and tipped by 1-2 teeth; dorsal sporophylls with upper surfaces green and cells as in median leaves, including stomata, lower surfaces greenish and comprising elongate, sinuate-walled cells; ventral sporophylls with both surfaces greenish, comprising elongate, sinuate-walled cells. Megasporangia in 2 ventral rows or few and intermixed with microsporangia; megaspores yellow, mostly immature, rugulate-reticulate on proximal faces, reticulate on distal faces, microstructure not examined, ca. 200 µm. Microsporangia in 2 dorsal rows and on ventral rows or also in axil of median leaves immediately below strobili; microspores light orange, ornamentation and diameter not determined.

Habitat and distribution.

Selaginella stomatoloma is an epipetric species known only from the state of Pará in Brazil. It grows in dense lowland to premontane wet forests, probably at 200-800 m.

Etymology.

The specific epithet is derived from the Greek stoma, meaning mouth, and loma, fringe or border; together these refer to the many stomata found on leaf margins.

Conservation status.

Selaginella stomatoloma is known only from three collections made in de Carajás National Forest, Brazil. This area is threatened by deforestation due to cattle ranching and large-scale mining ( Pinheiro et al. 2012). Therefore, Selaginella stomatoloma is considered Vulnerable (VU).

Additional specimens examined

(paratypes). BRAZIL. Pará: Canaã dos Carajás, S11D, [ca. 06°23'08"S, 50°18'58.24"W], 23 May 2012, Salino et al. 15284 (BHCB, PMA), 27 Aug 2012, Salino et al. 15492 (BHCB, PMA).

Discussion.

The minute plant size, stomata along leaf margins (Fig. 10 ), and microsporangia in the axils of the median leaves near the strobili are features that Selaginella stomatoloma shares with Selaginella saltuicola . They differ, however, by the characters discussed in the diagnosis.

The presence of stomata along leaf margins seems to be a more common feature in Selaginella than previously realized. This distribution was shown to occur in several species by, for example, Harvey-Gibson (1897), Schulz et al. (2010), Youguang and Tan (2013), and Valdespino et al. (2015), and are described here in Selaginella nanuzae (Fig. 1 , 2 ), Selaginella neospringiana (Fig. 4 ), Selaginella pellucidopunctata (Fig. 7 , 8 ), Selaginella stomatoloma (Fig. 10 ), and Selaginella trygonoides (Fig. 12 ), as well as being present on the outer margin of median leaves of Selaginella roraimensis Baker (see Fig. 11C in Alston et al. 1981: 284, shown as Selaginella scintillata Alston). Youguang and Tan (2013) hypothesized that leaf marginal stomata were non-functional; however, the widespread occurrence of this feature in morphologically distinct species from diverse regions of the world indicate the contrary, particularly when one considers their fundamental role in plant physiology. It seems evolutionarily inefficient for Selaginella to develop leaf marginal stomata (as well as on other parts of the lamina), besides those along the midribs, if they were not active in playing key roles in plant photosynthesis. In the absence of experimental evidence to the contrary, they are here considered functional. Nevertheless, these competing explanations for the distribution and physiological importance of stomata on Selaginella highlight the need for detailed experimental studies, to address functional issues.

Figures

Figure 1. Selaginella nanuzae Valdespino. A Section of upper surface of stem B Upper surface of median leaf C Close-up of base and proximal portion of median leaf, upper surface; note marginal (a) and submarginal (b) stoma, and outer base tufted with long cilia (c) D Close-up of distal portion and apex of median leaf, upper surface E Section of upper surface of stem F Close-up of outer half of median leaf, upper surface G Close-up-of inner half of median leaf, upper surface H Lower surface of median leaf. A-H taken from the holotype, Salino et al. 7788 (PMA).

Figure 2. Selaginella nanuzae Valdespino. A Section of lower surface of stem B Lower surface of lateral leaf C Close-up of base and distal portion of lateral leaf, lower surface D Close-up of acroscopic half of lateral leaf near base, lower surface E Close-up of distal portion and apex of lateral leaf, lower surface F Close-up of portion of basiscopic margin of lateral leaf near apex, lower surface; note marginal stoma (a) G Upper surface of lateral leaf H Close-up of upper surface of lateral leaf. A-H taken from the holotype, Salino et al. 7788 (PMA).

Figure 4. Selaginella neospringiana Valdespino. A Section of upper surface of stem B Upper surface of median leaf C Close-up of base and proximal portion of median leaf, upper surface D Close-up of distal portion and apex of median leaf, upper surface E Section of lower surface of stem F Lower surface of lateral leaf; note marginal stoma (a) G Close-up of proximal portion and base of lateral leaf, lower surface; note marginal stoma (a) on basiscopic margin and on outer margin of median leaf (far, lower right) H Close-up of distal portion and apex of lateral leaf, lower surface; note marginal stoma (a). A-H taken from the isotype, Glaziou 11723 (PMA).

Figure 7. Selaginella pellucidopunctata Valdespino. A Section of upper surface of stem B Upper surface of median leaf C Close-up of base and proximal portion of median leaf, upper surface; note marginal stoma (a) on outer margin D Close-up of median leaf, distal region, upper surface E Close-up of apex of median leaf, upper and lower surfaces; note marginal stoma (a) on basiscopic margin of lateral leaf, upper surface F Upper surface of lateral leaf; note marginal stoma (a) on basiscopic margin and submarginal tooth (b) G Close-up of base and proximal portion of lateral leaf, upper surface; note marginal stoma (a) on basiscopic margin H Close-up of distal portion and apex of lateral leaf, upper surface; note submarginal tooth (b). A-H taken from the isotype, Oliveira 1094 (PMA).

Figure 8. Selaginella pellucidopunctata Valdespino. A Section of lower surface of stem B Lower surface of lateral leaf C Close-up of distal portion and apex of lateral leaf, lower surface; note elongate, straight-walled, and papillate cells (idioblasts) D Close-up of lateral leaf, lower surface; note elongate, straight-walled, and papillate cells (idioblasts) E Strobilus, upper surface; note dorsal (Ds) and ventral (Vs) sporophyll F Dorsal sporophylls, adaxial- (F- 1) and abaxial surfaces (F- 2); note acroscopic margin (Ma) and basiscopic margin (Mb), this usually referred to as laminar flap (lf), stomata (a) throughout lamina and midrib, as well as tooth-like projections (b) on midrib and lamina, abaxial (upper) surface, marginal tooth projections (c), and ligule (d) G Strobilus, lower surface; note dorsal- (Ds) and ventral (Vs) sporophyll H Ventral sporophyll, adaxial (lower) surface. A-H taken from the isotype, Oliveira 1094 (PMA).

Figure 10. Selaginella stomatoloma Valdespino. A Section of upper surface of stem B Upper surface of median leaf C Close-up of base and proximal portion of median leaf, upper surface; note marginal (a) and submarginal stomata (b) D Close-up of proximal portion and apex of median leaf, upper surface; note marginal (a) and submarginal (b) stomata E Section of lower surface of stem F Lower surface of lateral leaf; note marginal stomata (a) G Close-up of base and proximal portion of lateral leaf, lower surface; note marginal (a) and submarginal (b) stomata H Upper surface of lateral leaf. A-H taken from the holotype, Almeida et al. 2518 (PMA).

Figure 11. Selaginella trygonoides Valdespino. A Section of upper surface of stem B Upper surface of median leaf; note submarginal stomata (a) on inner half of the lamina C Close-up of inner margin of median leaf, upper surface; note submarginal stomata (a) D Close-up of median leaf upper surface; note papillae on cell lumen E Upper surface of median leaf; note submarginal stomata on inner half of the lamina F Close-up of base, portion of inner margin and inner half of lamina (note stomata), and portion of outer margin and outer half of lamina of median leaf, upper surface G Upper surface of lateral leaf and portion of median leaves, upper surface H Close-up of distal portion and apex of lateral leaf, upper surface. A-H taken from the holotype, Almeida et al. 1994 (PMA).

Figure 12. Selaginella trygonoides Valdespino. A Section of lower surface of stem B Lower surface of lateral leaf C Close-up of base and proximal portion of lateral leaf, lower surface; note marginal stomata (a) D Close-up of distal portion and apex of lateral leaf, lower surface E Lower surface of axillary leaf and portions of lateral leaves F Upper surface of lateral leaf G Close-up of base and proximal portion of lateral leaf, upper surface H Close-up of distal portion and apex of lateral leaf, upper surface; note marginal stoma (a). A-H taken from the holotype, Almeida et al. 1994 (PMA).