Tetramerium vargasiae T.F. Daniel & Cruz Durán, 2016

Daniel, Thomas F. & Durán, Ramiro Cruz, 2016, Tetramerium vargasiae (Acanthaceae), a New Species from the Basin of the Río Balsas in Guerrero, Mexico, Proceedings of the California Academy of Sciences 63 (4), pp. 159-162 : 159-162

Tetramerium vargasiae T.F. Daniel & Cruz Durán , sp. nov.

TYPE. MEXICO: Guerrero: Mpio. Huitzuco de los Figueroa , 0.7 km NE de San Francisco Ozomatlán [ca. 17°56ʹ0.63ʺN, 099°19ʹ37.41ʺW], 650 m, bosque tropical caducifolio, 30–III–1990 (flr, frt), A. Vargas P. 288 (holotype: FCME!) .

Tetramerium vargasiae differs from congeners by the combination of its shrubby habit, linear leaves, pubescent (eglandular trichomes only) and entire bracts that are 16–19 mm long, 5-lobed calyx, pseudopapilionaceous and white (with purple markings) corollas, and glabrous capsules that are 7 mm long.

Shrubs to 1 m tall; older stems with bark exfoliating in strips; young stems ± terete, ± evenly pubescent with antrorse to antrorsely appressed eglandular trichomes 0.05– 0.2 mm long, nodes more densely pubescent. Leaves (immature; plants mostly leafless during anthesis) subsessile (petioles to 2 mm long), blades linear, sometimes ± conduplicate, 10–17 mm long, 0.6– 0.9 mm wide, length:width = 16.7–18.9, both surfaces and margin covered with antrorsely appressed eglandular trichomes 0.05– 0.2 mm long, only midvein evident. Inflorescence of terminal (sometimes terminating short axillary branches) and congested spikes to 46 mm long, 14–19 mm across (measured flat) near midspike, rachis densely and evenly pubescent with flexuous to antrorse to antrorsely appressed eglandular trichomes to 0.5 mm long, median internodes 6 mm long. Bracts ± coriaceous, lanceolate to lance-elliptic, 16–19 mm long, 1.8– 3.2 mm wide, obscurely to ± prominently and palmately 3-veined, apically straight, erect, and mucronate, mucro 0.5– 0.6 mm long, abaxial surface densely pubescent with antrorse to antrorsely appressed eglandular trichomes to 0.4 mm long, margin densely ciliate with spreading-flexuous, silky eglandular trichomes to 2.5 mm long (at least some trichomes> 1 mm long). Bracteoles lance-subulate, 9–14 mm long, 0.8– 1.1 mm wide, only midvein evident (sometimes obscure), abaxial surface and margin pubescent like bracts. Flowers sessile. Calyx 5-lobed, 6.5–8. 5 mm long, lobes lance-subulate to subulate, 6–7 mm long, 0.4–0.5 mmm wide, abaxial surface and margin pubescent like bracteoles. Corolla pseudopapilionaceous, white with purple markings on upper lip, 20 mm long, externally glabrous, tube 10.5 mm long, upper lip obovate, 9.5 mm long, 2.5 mm wide, lower lip 9 mm long, lower-central lobe conduplicate, 7 mm long, 4.6 mm wide, lateral lobes obovate, 7 mm long, 3.5 mm wide. Stamens ca. 7 mm long, thecae ca. 1.2 mm long. Capsules 7 mm long, glabrous, stipe 2.5 mm long, head 4.5 mm long. Seeds not seen.

PHENOLOGY.— Flowering and fruiting: March.

DISTRIBUTION AND HABITAT.— Endemic to Mexico where it is known only from the arid portion of the basin of the Río Balsas of north-central Guerrero in a region of tropical deciduous forest at 650 m elevation.

CONSERVATION ASSESSMENT.— Tetramerium vargasiae is known from a single collection from a population that was not observed during this study. The collector of the type indicated that only a few plants were observed at that site. Given the lack of additional information, this species is assessed as Data Deficient ( DD) according to IUCN guidelines ( IUCN 2014 ).

Although Tetramerium vargasiae is incompletely known, it is highly distinctive. It pertains to Daniel’s (1986) sect. Tetramerium and resembles T. tetramerioides (Lindau) T.F. Daniel from southeastern Oaxaca (previously known only from the type, but recently rediscovered in the vicinity of the type collection) in several characteristics, including: shape of the bracts and bracteoles, marginal pubescence of the bracts, number of calyx lobes, color and shape of the corolla, and size and surface vesture of the capsule. These two species can be distinguished by the characters noted in the following key:

1a. Young stems ± evenly pubescent with antrorse to antrorsely appressed eglandular trichomes 0.05– 0.2 mm long; leaves (immature) subsessile (petioles to 2 mm long), blades linear, length:width = 16.7–18.9; spikes 14–19 mm wide (measured flat) near midspike, rachis pubescent with eglandular trichomes; bracts 16–19 mm long, abaxial surface densely pubescent with antrorse to antrorsely appressed eglandular trichomes to 0.4 mm long; bracteoles 9–14 mm long; calyx 6.5–8. 5 mm long; corolla 20 mm long; Guerrero ................ T. vargasiae

1b. Young stems ± bifariously pubescent with an understory of glandular trichomes 0.05– 0.2 mm long and an overstory (absent on some internodes) of flexuose eglandular trichomes 0.2– 0.7 mm long; leaves subsessile to petiolate (petioles to 15 mm long), blades lance-ovate, length:width = 2.2–3.8; spikes 3–7 mm wide (measured flat) near midspike, rachis pubescent with glandular and eglandular trichomes; bracts 7–10 mm long, abaxial surface pubescent with an inconspicuous understory of glandular trichomes 0.05– 0.2 mm long and a sparse overstory (especially along the midvein) of flexuose eglandular trichomes to 1.5 mm long; bracteoles 6–8 mm long; calyx 3. 2–4 mm long; corolla 14–15 mm long; Oaxaca ..... T. tetramerioides

This species is named in honor of the collector of the type, Andira Vargas Pérez, who collected plants for FCME between 1989 and 1990 during a study of the flora and vegetation in the eastern part of the basin of the Río Basas in Guerrero.