Selaginella squamulosa Valdespino, 2017

Valdespino, Ivan A., 2017, Novel fern- and centipede-like Selaginella (Selaginellaceae) species and a new combination from South America, PhytoKeys 91, pp. 13-38 : 17-21

Selaginella squamulosa Valdespino sp. nov. Figures 6 , 7 , 8 , 9 , 10

Diagnosis.

Selaginella squamulosa is set aside from similar S. psittacorhyncha and S. vernicosa by its median leaves upper surfaces with 10 (vs. with 25 in S. psittacorhyncha and 35 in S. vernicosa ) stomata along the midribs. It differs further from S. psittacorhyncha by its lateral leaf acute (vs. obtuse) apices and hyaline (vs. greenish) margins and median leaf bases oblique (vs. truncate) and from S. vernicosa by the median leaf upper surfaces made up of quadrangular and rectangular (vs. undistinguishable, somewhat appearing quadrangular or elongate) papillate cells and lateral leaf margins on acroscopic side serrate to denticulate (vs. short-ciliate, at least along proximal ⅔) and on basiscopic side sparingly denticulate or entire to slightly denticulate distally (vs. short-ciliate at least along proximal ⅓).

Type.

Venezuela - Brazil. Venezuelan , Brazilian frontier, Planicie de Zuluaga, Río Titirico, 2300 m, 10-15 Oct 1970, J.A. Steyermark 103872 (holotype: NY; isotypes: MO, PMA) .

Description.

Plants terrestrial, epiphytic or epipetric. Stems creeping, stramineous, 10-20 cm long, 0.4-0.8 mm diam., non-articulate, often flagelliform, not stoloniferous, 1-2(3)-branched. Rhizophores axillary along proximal ½ of stem, filiform, 0.1 to 0.2 mm diam. Leaves dimorphic, coriaceous. Lateral leaves distant to imbricate towards stem and branch apices, ascending, broadly deltate-ovate, broadly ovate or ovate-elliptic, (1.0)1.3-1.7 × 0.8-1.7 mm; bases rounded, acroscopic bases overlapping the stem, basiscopic bases free from the stem; margins hyaline, made up of a band 2-4 cells wide, the cells elongate and papillate, parallel to margin, papillae in a single row over cell lumen, acroscopic margins serrate to denticulate, basiscopic margins sparingly denticulate or entire to slightly denticulate distally; apices broadly acute to acute, tipped by 2-4 teeth; both surfaces without idioblasts, upper surfaces mostly glabrous but with short hairs on submarginal and marginal sections of basiscopic half of the lamina, made up of quadrangular to rectangular, irregularly-walled, papillate or not cells, papillae 5-10 over cell lumen arranged in 2 or 3 rows, midribs not prominent, without stomata, lower surfaces glabrous, made up of elongate or asymmetric, straight or slightly sinuate-walled, papillate cells, papillae 8-20 over cell lumen arranged in 2 or 3 rows, midribs raised and prominent at mid-distal section of lamina, stomata concentrated on raised portion of midribs. Median leaves distant to imbricate towards stem and branch tips, ascending and, on branches, they may arise at ca. 45° angle, ovate to ovate-deltate, 1.0-1.5 × 0.6-1.0 mm; bases oblique, inner bases truncate to rounded, outer bases ventricose and often tufted with 2-8 very short hair or teeth; inner margins narrowly hyaline, made up of a band 1 or 2 cells wide, the cells elongate and papillate, parallel to margin, papillae in a single row over cell lumen, serrate to denticulate, outer margins greenish, denticulate at proximal ¼, otherwise sparingly denticulate or entire along middle and denticulate at distal ¼; apices acute, tipped by 2-4 teeth; both surfaces without idioblasts, upper surfaces mostly glabrous but occasionally with short hairs near marginal, submarginal and submedial section of outer half and on submedial section of inner half near distal ¼, made up of quadrangular or with some rectangular, irregularly-walled, papillate cells, papillae 5-10 over cell lumen arranged in 2 or 3 rows, midribs raised and prominent or bevelled specially at mid-distal section of each laminae, stomata concentrated on raised portion of midribs and some marginal on lower ½ of outer margins, lower surfaces glabrous, made up of elongate or asymmetric, straight or slightly sinuate-walled cells, midribs not prominent. Axillary leaves similar to lateral leaves. Strobili terminal and single on branch tips, quadrangular, 0.5-5 mm long. Sporophylls monomorphic, without a laminar flap, ovate to ovate-elliptic, 0.9-1.3 × 0.5-1.3 mm, with a keel along midrib on upper surfaces; base rounded; margins greenish, minutely denticulate to entire; apices acute; both surfaces without conspicuous idioblasts, both surfaces glabrous; dorsal sporophylls with upper surfaces green, except for the half that overlaps the ventral sporophylls where it is hyaline, lower surfaces greenish-hyaline; ventral sporophylls with both surfaces greenish-hyaline. Megasporangia one or two at the base of ventral rows; megaspore yellow, rugulate-reticulate on proximal faces with fissurate microstructure, reticulate-granular on distal faces with granulose and perforate microstructure, 410-445 μm diam. Microsporangia in dorsal rows and distal ¾ of ventral rows; microspores deep orange, proximal and distal faces not studied and not measured.

Habitat, distribution and phenology.

Selaginella squamulosa grows as a terrestrial, epiphytic or epipetric plant on open slopes to cliff base, in rills and wet depressions of swampy savannas or on scrub dominated forests at 1950-2743 m; it is known from the Guiana Highlands in Cerro de la Neblina, Amazonas State of Venezuela and in Río Cuaburí, Amazonas State of Brazil and found fertile from October through to February.

Etymology.

The specific epithet derives from the Latin " squamulosus ", meaning minutely scaly and refers to the tiny, stiff leaves that resemble small scales.

Conservation status. Selaginella squamulosa is known from two distinct localities at high elevation in isolated tepuis in the Amazon basin of Venezuela and Brazil where human presence is scarce and immediate threats have not been reported. Therefore, it is tentatively considered of Least Concern (LC) according to IUCN (2012) categories and criteria.

Additional specimens examined (paratypes).

VENEZUELA. Amazonas: Depto. Rio Negro , Camp VII, Cerro de la Neblina, 5.1 km NE of Pico Phelps (= Neblina), 21.5 km E [of] Neblina Base Camp, ca. 2150 m, 5 Feb 1985, Beitel 85161 (NY-2 sheets, PMA), Neblina Massif, Camp 12, 1950 m, 26-27 Feb 1985, Boom et al. 6011 (NY, PMA, UC) . BRAZIL. Amazonas: Río Negro, Rio Cuaburi , 8500-9000 ft [2591-2743 m], 2 Dec 1965, Maguire et al. 60466 (NY) .

Discussion.

Selaginella squamulosa is distinguished by its centipede-like habit with slender and creeping stems, rhizophores restricted to the lower halves of the stems or often present on flagelliform stems and branches (i.e. Steyermark 103872, NY), coriaceous, scaly-like leaves with raised and prominent midribs on the lower and upper surfaces of the lateral and median leaves, respectively and acute leaf apices. In addition, the midribs on the upper surfaces of the median leaf are straight to strongly arcuate. In the latter case, the inner half of each leaf lamina becomes slightly wider than the outer one. It is further strikingly distinct by having the lateral leaf acroscopic halves on lower surfaces twice as wide as the basiscopic ones. Furthermore, as noted in other Selaginella species, on a duplicate specimen of S. squamulosa (i.e. Steyermark 103872, MO), a rhizophore becomes a leaf-bearing shoot. Remarkably, Boom et al. 6011 (NY, PMA, UC) has a more slender habit with the upper leaf surfaces hispidulous. Apparently, these hairs become caducous since they were not observed in a similar collection (i.e. Beitel 85161, NY, PMA) or in the more coriaceous form represented by the type.

The holotype and an isotype of Selaginella squamulosa at NY and MO, respectively, were originally identified as S. cruegeri Jenman vel aff., which is a synonym of S. minima Spring. The latter species differs most noticeably from S. squamulosa by its ascending (vs. creeping) habit, chartaceous (vs. coriaceous) leaves, median leaf with broadly hyaline margins (vs. inner margins narrowly hyaline and outer margins greenish) and white (vs. yellow) megaspores. A paratype of S. squamulosa (i.e. Boom et al., 6011, NY, PMA, UC) was determined as S. rhodostachya Baker vel aff. Nevertheless, S. squamulosa is easily set aside from S. rhodostachya by its coriaceous (vs. chartaceous) leaves, oblique (vs. rounded to truncate) median leaf bases with the outer bases ventricose (vs. rounded) and ovate (vs. ovate-elliptic) lateral leaf with its acroscopic margins, as well as both margins of the median leaf serrate to denticulate (vs. often long-ciliate). Another of the paratypes of S. squamulosa (i.e. Maguire et al. 60466, NY) was determined as S. brachyclada Baker. However, it differs from the latter by having the inner and outer margins of the median leaf narrowly hyaline and greenish, respectively (vs. both margins widely hyaline) and serrate to denticulate (vs. faintly denticulate), oblique (vs. truncate) bases, ovate or ovate-elliptic (vs. ovate-cordate) lateral leaf, which is distinctly wider at the middle (vs. at the base), ascending (vs. spreading) and deep yellow (vs. white to light-yellow) megaspores that lack (vs. have) a distinct equatorial flange.

Selaginella squamulosa is part of the " Selaginella vernicosa group" and, amongst these, it is morphologically close to S. psittacorhyncha and S. vernicosa . It differs from these two species by the characters discussed under the diagnosis and by its median leaf with the midribs raised at the distal ½ of the laminae but not properly extending into the apices (vs. extending into the apices) with the upper surfaces occasionally puberulent (vs. glabrous). Selaginella squamulosa differs from S. arrecta by its median and lateral leaf apices broadly acute to acute (vs. long-acuminate to aristate), median leaf inner margins narrowly (vs. widely) hyaline, which consists of 1 or 2 (vs. 3-5) elongate cells wide and ca. 10 stomata on raised midribs (vs. up to 85 stomata, widespread on central portion of lamina). In addition, in S. squamulosa , 2-4 teeth tip the acute apices, whereas the acuminate or aristate apices of S. arrecta are made of 6-10, narrowly elongate and papillate cells. Selaginella squamulosa differs from S. roraimensis , S. marahuacae and S. scalariformis by its narrowly ovate-deltate or ovate (vs. ovate-oblong or oblong in S. roraimensis and ovate-elliptic in S. marahuacae and S. scalariformis ) lateral leaves with midribs on lower surfaces distinctly raised (vs. plane in profile). Selaginella squamulosa is further separated from S. roraimensis by the lateral leaf basiscopic margins extended (vs. slightly reflexed), from S. marahuacae by its acute (vs. shortly acuminate) median leaf apices and from S. scalariformis by its distant to imbricate and ascending (vs. distant and patent) lateral leaves.

Figures

Figure 6. Selaginella squamulosa Valdespino. Holotype, Steyermark 103872 (NY).

Figure 7. Selaginella squamulosa Valdespino. A Habit B Upper surface of stem showing median leaves C Lower surface of stem showing lateral leaves and axillary leaf D Close-up of strobili (apices of branches), upper surface. A-D line drawings of holotype, Steyermark 103872 (NY). Illustration made by Ruben Lozano.

Figure 8. Selaginella squamulosa Valdespino. A-B Habit C Upper surface of stem showing median leaves D Lower surface of stem showing lateral leaves and axillary leaf E Close-up of distal portion of stem, upper surface. A-E line drawings of paratype, Boom et al. 6011 (NY). Illustration made by Ruben Lozano.

Figure 9. Selaginella squamulosa Valdespino. A Section of upper surface of stem B Close-up of median leaf, upper surface; note, elongate, idioblast-like marginal cells on inner margin and submarginal and marginal stomata (a) along proximal 1 / 2 of outer margin and hairs (b) on lamina surface C Close-up of mid-distal portion of median leaf, upper surface (same leaf shown in B); note, elongate, idioblast-like marginal cells on inner margin, papillae on each cell lumen and hairs (b) on lamina surface D Section of lower surface of stem E Close-up of lateral leaf, lower surface F Close-up of section of acroscopic half of lateral leaf; note, papillae on cells lumen and marginal, idioblast-like and papillate cells. A-F taken from paratype, Boom et al. 6011 (NY).

Figure 10. Selaginella squamulosa Valdespino. A Megaspore, proximal face B Close-up of megaspore, proximal face C Megaspore, distal face D Close-up of megaspore, distal face. A-D taken from paratype, Boom et al. 6011 (NY).