Selaginella alstonii G. Heringer, Salino & Valdespino, 2015

Valdespino, Ivan A., Heringer, Gustavo, Salino, Alexandre, Goes-Neto, Luiz A. de Araujo & Ceballos, Jorge, 2015, Seven new species of Selaginella subg. Stachygynandrum (Selaginellaceae) from Brazil and new synonyms for the genus, PhytoKeys 50, pp. 61-99 : 64

Selaginella alstonii G. Heringer, Salino & Valdespino sp. nov. Figures 1 , 2

Diagnosis.

Selaginella alstonii resembles Selaginella acanthostachys Baker, from which it differs by having the upper surfaces of the lateral leaves glabrous (vs. hairy near basiscopic margins), median leaves acuminate to short-aristate (vs. long-aristate) with each acumen (arista) ¼ or less the lamina length (vs. arista ⅓- ½), with the outer and inner hyaline margins about the same width (vs. outer margin almost twice as wide as the inner one), and non stoloniferous stems (vs. stoloniferous).

Type.

BRAZIL. Minas Gerais: Santo Antônio do Itambé, Parque Estadual do Pico do Itambé, 18°23'50,4"S, 43°19'55,5"W, 1676 m, 5 Oct 2006, T.E. Almeida et al. 533 (holotype: BHCB!; isotype: PMA!).

Description.

Plants epipetric. Stems prostrate to ascending, greenish to stramineous, to 10 cm long, 0.3-0.6 mm diam., exarticulate, not flagelliform or stoloniferous, 2- or 3-branched. Rhizophores ventral, borne on the proximal ⅔ of stems, filiform, 0.1-0.2 mm diam. Leaves heteromorphic throughout, chartaceous, both surfaces glabrous, upper surfaces green, lower surfaces silvery green. Lateral leaves distant, spreading to slightly ascending, oblong to oblong-lanceolate, 1.1-2.0 × 0.4-1.0 mm; bases rounded, acroscopic bases overlapping stems, basiscopic bases free from stems; acroscopic margins on upper surfaces hyaline along proximal ½-¾ in a band 1 or 2 cells wide, the cells elongate and papillate parallel to margins, papillae in 1 row over each cell lumen, otherwise greenish distally with rounded to quadrangular, sinuate-walled cells, on lower surfaces hyaline in a band 2-5 cells wide, the cells elongate and papillate parallel to margins, papillae in 1 row over each cell lumen, short-ciliate along proximal ⅓- ½, otherwise serrate distally, basiscopic margins greenish on upper surfaces with rounded to quadrangular, sinuate-walled cells and on lower surfaces with elongate, sinuate-walled cells, entire along proximal ¾ and serrulate on distal ¼; apices acute to slightly cuspidate, each cusp 0.02-0.03 mm, tipped by 1-3 teeth; upper surfaces comprising rounded to quadrangular, sinuate-walled cells, without idioblasts or stomata, lower surfaces comprising elongate, sinuate-walled cells, with some obscure, papillate idioblasts and stomata along central portion of midribs and along basiscopic margins. Median leaves distant to slightly imbricate near the branch tips, ascending, elliptic to elliptic-lanceolate or ovate-elliptic, 0.7-1.4 × 0.4-0.7 mm; bases oblique; margins hyaline in a band 2-5 cells wide, the cells elongate and papillate parallel to margins, papillae in 1 row over each cell lumen, inner margins serrate to short-ciliate, outer margins entire along proximal ½, otherwise serrate to short-ciliate distally; apices acuminate to short-aristate, each acumen (arista) 0.15-0.2 mm, entire or obscurely tipped by 1-3 teeth; both surfaces without conspicuous idioblasts, upper surfaces comprising quadrangular to rounded, sinuate-walled cells, some of these covered by 10-20 papillae, with stomata along midribs on distal half and submarginal and marginal along proximal half of outer margins, lower surfaces comprising elongate, sinuate-walled cells, without stomata. Axillary leaves similar to lateral leaves but with both margins ciliate along proximal ¼, otherwise short-ciliate to serrate distally. Strobili terminal on branch tips, compact, quadrangular, 1.5-4.0 mm. Sporophylls monomorphic, without a laminar flap, ovate to ovate-lanceolate, 0.7-1.1 × 0.4-0.6 mm, each with a dentate (teeth often caducous) keel along distal ½ of the midribs; bases rounded; margins narrowly hyaline, serrate; apices acute, entire or obscurely tipped by 1-3 teeth; dorsal sporophylls with upper surfaces green and cells as in median leaves, except for the half that overlaps the ventral sporophylls, there hyaline with elongate, sinuate-walled cells, lower surfaces silvery green and comprising elongate, sinuate-walled cells; ventral sporophylls with both surfaces hyaline to faintly greenish hyaline, comprising elongate, sinuate-walled cells. Megasporangia in proximal portion in 2 ventral rows; megaspores cream, with a cristate equatorial flange, rugulate on proximal faces, reticulate with low, cristate ridges on distal faces, with areolate-perforate microstructure on both faces, 250-300 μm diam. Microsporangia in 2 dorsal rows and, in distal portion, also in 2 ventral rows; microspores orange, psilate marginally and verrucate-rugulate towards the center with psilate microstructure on proximal faces, clavate (Fig. 2G, H ) or echinulate to baculate (if apices of projected elements broken off, Fig. 2F, H ) with striate to striate-reticulate microstructure on distal faces, 27-33 μm diam.

Habitat and distribution.

Selaginella alstonii is epipetric on rocky caves in Campos Rupestres vegetation; the type and paratype were collected at an elevation range of 1676-1810 m. The species is known only from Parque Estadual do Pico do Itambé in Serra do Espinhaço, Minas Gerais, Brazil, where it may be a local endemic.

Etymology.

Selaginella alstonii is named for Arthur Hugh Garfit Alston (1902-1958), a British pteridologist and one of the world’s authorities on the genus Selaginella .

Conservation status.

There is limited information on the conservation status and range distribution of Selaginella alstonii . Nevertheless, given that the localities where this species is presently known are located within the Espinhaço Mountain Range, a habitat threatened by human activities ( Rapini et al 2008), we tentatively consider it vulnerable (VU) according to IUCN (2012) categories and criteria.

Additional specimen examined (paratype).

BRAZIL. Minas Gerais: Santo Antônio do Itambé, Parque Estadual do Pico do Itambé, 18°23'50,4"S, 43°19'55,5"W, 1810 m, 5 Oct 2006, Almeida et al. 535 (BHCB).

Discussion.

Selaginella alstonii belongs to subg. Stachygynandrum and is characterized by its oblong to oblong-lanceolate lateral leaves with acroscopic margins short-ciliate along proximal ⅓- ½ and elliptic to elliptic-lanceolate or ovate-elliptic median leaves with oblique bases (Fig. 1 ). Dried specimens of Selaginella alstonii tend to develop a groove along midribs of lateral leaves (Fig. 1A ), but it remains to be confirmed if this is a character observed in living plants or an artifact when plants are dried. The surfaces of the median and lateral leaves of Selaginella alstonii do not show conspicuous idioblasts when observed with a stereoscope, but on SEM micrographs, idioblast-like, papillate elongate cells are observed on the lower surfaces of lateral leaves, with papillae in 1 row over each cell lumen, parallel to the midribs (Fig. 1D ). Additionally, in some median leaves, the outer bases have 2-4 short cilia. In some plants of Selaginella alstonii , as well as in Selaginella saltuicola (which see for discussion), we observed vegetative growth from the tips of some strobili.

Selaginella alstonii resembles Selaginella acanthostachys from Colombia, Ecuador, and Peru; however the characters given in the diagnosis separate them. Among other species of Selaginella from Minas Gerais, Selaginella alstonii may be confused with Selaginella decomposita Spring because of their similar texture and shape of the lateral leaves. Selaginella decomposita , however, has an ascending to erect habit and is a more robust plant.

Figures

Figure 1. Selaginella alstonii G. Heringer, Salino & Valdespino. A Section of upper surface of stem B Upper surface of median leaf C Section of lower surface of stem D Lower surface of lateral leaf. A-D taken from isotype, Almeida et al. 533 (PMA).

Figure 2. Selaginella alstonii G. Heringer, Salino & Valdespino. A Megaspore proximal face B Close-up of megaspore proximal face surface C Megaspore distal face D Close-up of megaspore distal face surface E Microspore proximal face F Microspore distal face G Close-up of microspore distal face surface H Close-up of microspore equatorial view surface A-H taken from isotype, Almeida et al. 533 (PMA).