Elytraria serpens Greuter & R. Rankin, 2021

Greuter, Werner & Rodriguez, Rankin, 2021, On a noteworthy habitat type in the savannahs of Central Cuba and a remarkable new species of Elytraria (Acanthaceae), PhytoKeys 177, pp. 117-124 : 117

Elytraria serpens Greuter & R. Rankin sp. nov.

Type.

Cuba central, Prov. Villa Clara, "Municipio Corralillo: entre Las Cañas y el arroyo Clarita, alt. 85 m, 22°50'55"N, 80°28'22"W. Sabana en suelo mocarrero (con capa superficial de glomérulos ferralíticos)”, 4-III-2019, Greuter 29687, R. Rankin, I. Castañeda & A. Pérez Obregón (holotypus PAL-Gr, isotypi: B #101145054 [Fig. 3 ], HAJB, JE, ULV) .

Planta perennis herbacea acaulis,foliis omnibus basalibus in rosulam humo accumbentem congestis. Folia anguste spatulata, 2-4 cm longa et 0.6-0.8 mm lata, subplana vel saepius transverse undulata, glabra vel praecipue in latere abaxiali ad costam ± villosa, petiolo brevi (2-3 mm) pallide brunneo-villoso. Pedunculi graciles, 3-12 ex axillis rosulae basalis orientes, unus alterve brevis arcuate adscendens folia vix superans, praecipui autem tortuosi, stolonorum modo longe (20 cm vel ultra) subterranee repentes, omnes dense bracteis sterilibus squamiformibus subimbricatis obsiti. Bracteae steriles sessiles, amplexicaules, subterraneae, extus glabrae, margine antrorsum ciliolatae, intus apicem versus minutissime glanduloso-papillosae; inferiores (subterraneae) ovato-triangulares, subacutae, stramineae, minimae (1-2 mm longae), superiores (aereae) gradatim majors, 2-3 mm longae, acuminatae, virentes. Ad apicem pedunculorum nonnullorum gemmae jam florendi tempore foliiferae sed nondum radicantes conspiciuntur. Inflorescentiae spiciformes, densae, 1-2 cm longae, bracteis imbricatis indutae, ad apicem pedunculorum singulae vel binae ternaeve congestae. Bracteae floriferae bracteis sterilibus superioribus non dissimiles sed majores, virides, ca. 6 mm longae et 2.5 mm latae, ovato-triangulares, acuminatae et breviter aristatae, infra glabrae sed apicem versus sub lente retrorso-pubescentes, margine cuncto antrorse ciliatae, intus minute glanduloso-papillosae. Flores pauci, singulatim florentes. Calyx ca. 5 mm longus, bracteolis binis suffultus. Bracteolae bracteis conformes sed minores et angustiores, ca. 4 mm longae et 0.7 mm latae. Sepala 4 (sed sepalum abaxiale binerve et apice bidentatum), bracteolis majora, ca. 5 mm longa et 1.2 mm lata, extus glabra, margine apicem versus fimbriato-ciliata, intus minute antrorso-puberula. Corolla parva (ca. 3 mm longa), hypocrateriformis, albida, tubo subrecto, inconspicue sigmoideo, ca. 2.5 mm longo et 0.6 mm crasso, limbo subregulari, 1.5 mm diámetro, lobis expansis truncato-retusis. Capsulae (paucae perfectae) lineari-obpyriformes, ca. 4 mm longae et 1.2 mm latae, bivalvatae, valvis post dehiscentiam basi connatis apice arcuatim divergentibus. Semina (submatura?) ca. 12, quae dehiscencia peracta in capsula inclusa manent, pallide brunnea, glabra (etiamsi in acua inmersa), subanguloso-ellipsoidea, ca. 0.6 mm longa et 0.4 mm lata, sub lente rugulosa.

Amongst Cuban Acanthaceae , the two genera Elytraria and Stenandrium Nees stand out, being small stemless herbs with basal leaves forming a rosette and flowers in terminal spikes borne on scapiform peduncles that emerge directly from the basal rosette. According to Alain (1957) and other authors, these genera are best distinguished by the number of fertile stamens, 2 in the first and 4 in the second; but this character is not easily observed even when flowers are present. More obvious is the difference in the scapes or peduncles, which are naked in Stenandrium , but densely beset with small scaly bracts in Elytraria . In addition, the inflorescences of the latter genus are compact, surrounded by densely imbricate bracts, whereas, in Stenandrium , at least the lower flowers of each spike are distant from each other and their bracts do not overlap. Both genera have a major centre of diversity in the Caribbean. According to Greuter and Rankin Rodríguez (2017), seven taxa (species and subspecies) of Elytraria were known from Cuba, all endemic and 11 taxa of Stenandrium , nine endemic. Worldwide ( PoWo 2021), 22 taxa are accepted in Elytraria : the seven Cuban ones, plus one from Hispaniola, eight from continental America, four from the African continent (one of them also grows in eastern India) and two from Madagascar. The genus Stenandrium is larger (65 taxa) and less homogeneous, as it includes several species with elongated stems and opposite leaves; it presents a very similar distribution and diversification pattern: 15 taxa from the Caribbean islands, 11 of them present and nine endemic in Cuba, more than 31 species from the American continent (22 from South America); and 19 African species, 10 of them endemic to Madagascar ( PoWo 2021).

Most of the seven Cuban endemics of Elytraria have restricted ranges and five of the six species are threatened; one of them ( E. filicaulis ) is considered as Critically Endangered ( González-Torres et al. 2016). Borhidi and Muñiz (1978), who proposed a determination key for the six taxa known at that time, distinguish species with papery leaves and 5-merous calyx from the others, with membranous leaves and 4-merous calyx. However, our data and the descriptions of other authors ( Leonard 1934; Dietrich 1982) suggest that the calyx always consists of four free sepals, but with the abaxial one slightly wider, 2-nerved and apically bidentate, that takes the place of two concrescent sepals. According to label data and protologue indications, at least four of the Cuban taxa of Elytraria grow on ophiolitic substrates and can be considered serpentinophytes: E. cubana , E. filicaulis , E. planifolia subsp. planifolia and E. planifolia subsp. acunae . E. bissei and E. spathulifolia are considered calcicolous, while the habitat of E. shaferi , according to the collector, is an arid cliff-face in a serpentine area of Holguín (Sierra de Nipe, Woodfred mines).

In its vegetative features, Elytraria serpens is very similar to E. bissei of limestone areas of southern Guantánamo (Abra de Mariana), which, however, has leaves hairy on both sides and subsessile spikes not exceeding the basal rosette; and it is akin to E. shaferi , with which it shares the pubescence of the outer face of the flower bracts. The species most closely related to ours is E. cubana , for which the collector, on the label of the type specimen (Shafer 2948, NY), noted: "Lvs. flat on ground, among rocks in red soil, stony hillsides". In this species, with leaves of similar dimensions and shape to ours, the peduncles are decumbent and flexuous, but much shorter than in E. serpens , never subterranean, and the flower bracts, on the outside, are glabrous rather than pubescent.

In our opinion, Elytraria serpens evolved from plants similar to E. cubana by adapting itself to the particular edaphic conditions of its habitat. It takes advantage of the loose granular structure of the gravel layer that enables it to push its developing peduncles through it, hiding them underground, sheltered from the extreme drought and radiation at the surface, to produce apical buds at an appreciable distance from its origin, thus ensuring its vegetative spread. The specimens at hand suggest that fruit set is poor, perhaps due to inadequate pollination and that the explosive capsule dehiscence, normally ensuring seed dispersal in this family ( Greuter and Rankin Rodríguez 2010), is not fully functional.

Figures

Figure 3. Isotype of Elytraria serpens (B).