Selaginella saltuicola 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 : 73-77

Selaginella saltuicola Valdespino sp. nov. Figures 12 , 13

Diagnosis.

Selaginella saltuicola is morphologically close to Selaginella prasina Baker but differs from it by having median leaves on main stems ovate or ovate-elliptic (vs. oblong to oblong-elliptic), with acute (vs. obtuse) apices, distally entire (vs. toothed), inner margins entire (vs. dentate distally), narrowly hyaline (vs. green) with (vs. without) a band of 1-3 elongate and papillate cells, leaf bases rounded to oblique (vs. decurrent), strobili borne throughout the stems and weakly defined (vs. terminal and compact), with (vs. without) continuous, vegetative growth from the apices, sporophylls similar to (vs. well-differentiated from) vegetative leaves, and light-orange (vs. deep orange) megaspores.

Type.

BRAZIL. Mato Grosso: Chapada dos Guimarães, Gorge of Véu de Noiva [ca. 15°24'21"S, 55°50'12"W], [ca. 720 m] 17 Oct 1973, G.T. Prance et al. 19126 (holotype: NY!; isotypes: INPA!, PMA-fragment!).

Description.

Plants epipetric or epiphytic. Stems creeping, stramineous to green, 1.5-3 cm long, 0.05-0.2 mm diam., exarticulate, not flagelliform or stoloniferous, 1-branched. Rhizophores axillary, borne throughout stems, filiform, 0.05-0.1 mm diam. Leaves heteromorphic throughout, thin-membranaceous, both surfaces glabrous, upper surfaces green, lower surfaces silvery green. Lateral leaves distant or imbricate apically, patent to slightly ascending, ovate, ovate-elliptic or ovate-oblong, 0.9-1.5 × 0.5-0.8 mm; bases rounded, acroscopic bases slightly to strongly overlapping the stems, basiscopic bases free from the stems; acroscopic margins on upper surfaces greenish or narrowly hyaline, if the latter, in a band 1 or 2 cells wide, the cells elongate and papillate parallel to margins, papillae in 1 row over each cell lumen, on lower surfaces hyaline in a band 2-4 cells wide, the cells as on upper surfaces, entire or minutely serrulate along distal ¼, basiscopic margins on upper surfaces greenish on lower surfaces, narrowly hyaline marginally in a band 2-4 cells wide, the cells as along acroscopic hyaline margins, entire or inconspicuously denticulate throughout; apices rounded to broadly acute, entire or tipped by 1-3 teeth; upper surfaces comprising rounded to quadrangular, sinuate-walled cells, some of these on or near basiscopic and apical regions of the laminae covered by 2-4 papillae, without idioblasts and with stomata along margins, lower surfaces comprising elongate, sinuate-walled cells, some of these papillate and idioblast-like, papillae in 1 row over each cell lumen, with stomata irregularly distributed along midribs, as well as on acroscopic half of the laminae and on both margins (visible in both surfaces of the laminae). Median leaves distant or imbricate apically, ascending to spreading, ovate or ovate-elliptic, 0.6-0.9 × 0.4-0.5 mm; bases rounded or oblique, ventricose (i.e., swollen); margins narrowly hyaline in a band 1-3 cells wide, the cells elongate and papillate parallel to margins, papillae in 1 row over each cell lumen, entire; apices acute, entire (not distinctly tipped by teeth or cilia); both surfaces without idioblasts, upper surfaces comprising rounded to quadrangular, sinuate-walled cells, many of these covered by 2-4 papillae, with stomata throughout the laminae and some near submarginal region of the outer bases, lower surfaces comprising elongate, sinuate-walled cells, without stomata. Axillary leaves similar to lateral leaves. Strobili borne throughout the stems, weakly defined, lax, flattened, 1.0-2.0 mm. Sporophylls similar to or slightly differentiated from vegetative leaves, monomorphic to subdimorphic, without a laminar flap, ovate, 0.7-1.4 × 0.5-0.8 mm, each without a keel; bases rounded; margins narrowly hyaline, entire; apices acute, entire (not distinctly tipped by teeth or cilia); dorsal sporophylls with upper surfaces green and cells as in median leaves, except for the half that overlaps the ventral sporophylls, there hyaline to greenish hyaline with elongate, papillate, and slightly sinuate-walled cells, lower surfaces silvery green and comprising elongate, sinuate-walled cells; ventral sporophylls with both surfaces hyaline to greenish hyaline, comprising elongate, sinuate-walled cells. Megasporangia few in 1 ventral row; megaspores light-orange, mostly absent, proximal and distal faces not observed, not measured. Microsporangia in 2 dorsal rows and in 1 ventral row or few and in axils of median leaves; microspores deep orange, areolate-fossulate with granulate microstructure on proximal and distal faces, 25-31 µm.

Habitat and distribution.

Selaginella saltuicola is unique among other species here described by its apparent adaptation to very wet areas near waterfalls and perhaps even partially submerged in water along creek banks in Cerrado vegetation. At present, this species is known only from the high plateau of the Chapada dos Guimarães, Mato Grosso, Brazil, where it may be a local endemic, growing on wet rocks or wet logs at 600-720 m.

Etymology.

The epithet of the new species is derived from the Latin saltus, meaning jump, drop or fall and cola, meaning dweller, inhabitant, and alludes to it habitat near “cachoeiras” (waterfalls).

Conservation status.

Selaginella saltuicola seems to be restricted to the Chapada dos Guimarães area, where the Cerrado vegetation is dominant and severely threatened by human activities ( Oliveira-Filho and Martins 1991, Ratter et al. 1997, Strüssmann and Mott 2009). Selaginella saltuicola may therefore be tentatively considered vulnerable (VU), according to IUCN (2012) categories and criteria, at least until additional distributional and conservation status studies can be carried out.

Additional specimens examined (paratypes).

BRAZIL. Mato Grosso: Waterfall at first Igarapé after descending Chapada on road to Cuiabá, 600 m, 23 Oct 1973, Prance et al. 19336 (INPA, NY), 19337 (INPA, K, NY); Chapada dos Guimarães, Gorge of Véu de Noiva, 17 Oct 1973, Prance et al. 19123 (INPA, NY), 19127 (NY), 19128 (INPA, NY), 19136 (INPA, NY), 19138 (NY).

Discussion.

Selaginella saltuicola belongs to subg. Stachygynandrum and is morphologically similar to Selaginella prasina from Cuba, Selaginella salazariae Valdespino from Panama, and Selaginella undata Shelton & Caluff, from Cuba, because they share similar habit and overall vegetative leaf morphology, stomata throughout upper surfaces of median leaves, and midribs of lateral leaves restricted to ca. ¼ below apices. However, Selaginella undata (isotype: Shelton & Caluff 4514, B!) falls within the morphological range of Selaginella prasina and may be best considered conspecific with the latter. Selaginella saltuicola differs from Selaginella prasina by the characters of median leaf shape, apex type, inner margin color and projections, leaf base shape, strobilus morphology, and megaspore color, as discussed in the diagnosis, as well as by having ovate, ovate-elliptic, or ovate-oblong (vs. obovate) axillary leaves and many cells on the upper surfaces of median leaves covered by 2-4 (Fig. 12B ) [vs. without (Fig. 12E )] papillae. It differs from Selaginella salazariae in its median leaves ovate or ovate-elliptic (vs. obovate, obovate-elliptic, or broadly elliptic) with acute (vs. abruptly cuspidate to short-aristate) apices.

We note that Neotropical Selaginella species studied (i.e., Selaginella prasina , Selaginella salazariae , and Selaginella saltuicola ) that grow either partially underwater or constantly wetted by waterfalls, rivers, or creeks have numerous stomata distributed over the upper surfaces of median leaves (Fig. 12A, B, E ) and broadly acute to obtuse, rounded (Fig. 12A, C, D ) or truncate lateral leaves (Fig. 12F ). At present, it is not clear if the shared characters among those species might be the result of adaptation to a similar habitat (i.e., wet rocks or logs on waterfalls or stream banks) by convergent evolution or synapomorphies that may phylogenetically relate them.

In some plants of Selaginella saltuicola , as well as in some of Selaginella alstonii , we found strobili with continuous, vegetative growth from their apices. This condition was reported to occur in the genus by Hieronymus (1901), Williams (1931), Jermy (1990), and Valdespino (1993a, 1993b, 1995). In Selaginella , normally, fertile shoots (strobili) originate from the tips of vegetative shoots (i.e., stems and branches) in a "vegetative (V)/determinate fertile (F) growth pattern" or "V/F pattern," although in plants of some species, e.g., Selaginella decomposita and Selaginella saltuicola , microsporangial development was observed in axils of median leaves, similarly to what is seen in Selaginella denticulata (L.) Spring where mega- and microsporangia are found in axils of lateral leaves below the weekly differentiated strobilus (see images in Quiles 2015). In the phenomenon described for Selaginella saltuicola and Selaginella alstonii , however, the fertile growth becomes indeterminate and the apices of strobili revert to a vegetative condition in what could be termed a "V/indeterminate F/V growth pattern" or "V/F/V pattern" that is also found in other species such as Selaginella finitima Mickel & Beitel, Selaginella porphyrospora A. Braun, and Selaginella tenella (P. Beauv.) Spring in mainland in the Neotropics ( Valdespino 1995), Selaginella orbiculifolia Shelton & Caluff from Cuba ( Caluff and Shelton 2003), and Selaginella wangpeishanii Li Bing Zhang, H. He & Q. W. Sun from China, which Zhang et al. (2014) termed TST (where T is for trophophyll = vegetative leaf, and S is for sporophyll) arrangement of microphylls. In a third condition, the second vegetative growth of the V/F/V pattern of the shoot becomes fertile and indeterminate in a "V/F/ V/indeterminate F growth pattern" or “V/F/V/F” pattern, found for example in Selaginella correae Valdespino from Panama ( Valdespino 1993b), Selaginella oregana D.C. Eaton from temperate zones in western North America ( Valdespino 1993a), and Selaginella tuberculata Spruce ex Baker (e.g., Steyermark 75483, NY!) from South America. This V/F/V/F pattern consists of a shoot with alternating vegetative leaves, sporophylls, and vegetative leaves along the stems and is reminiscent of the pattern found in some species of Huperzia ( Lycopodiaceae ). Valdespino (1995) suggested these alternating patterns of vegetative stems and fertile shoot formation could be an adaptive strategy of Selaginella , or it could be a response to damage to the growing apices. In any case, hormones may probably mediate this phenomenon, which seems to be more common and found across geographically and phylogenetically different Selaginella taxa than previously acknowledged. The ecological advantages of such variation, phylogenetic significance, and possible genetic and/or hormonal origin remain to be determined.

Figures

Figure 12. Selaginella saltuicola 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 paratype, Prance et al. 19337 (NY). Selaginella prasina Baker E Upper surface of median leaf F Lower surface of lateral leaf E, F taken from Smith et al. 115583 (GH).

Figure 13. Selaginella saltuicola Valdespino. A Microspore proximal face B Microspore distal face A, B taken from holotype, Prance et al. 19126 (NY).