Tinnea gombea Zhigila, 2023

Zhigila, Daniel A., Aigbokhan, Emmanuel I. & Muasya, A. Muthama, 2023, Tinnea gombea (Lamiaceae), a new species from the Sudanian savanna region, Nigeria based on integrative evidence, PLoS ONE (e 0280550) 18 (3), pp. 1-13 : 8-11

Tinnea gombea Zhigila sp. nov.

( Fig 2 ). [urn:lsid:ipni.org:names:77311521–1]

Type

NIGERIA. Gombe State: Akko Local Government Area, in farmlands of the grassland Sudanian savanna, elevation 620 m, 10˚ 17’ 9.96"N, 11˚ 0’ 21.6"E, 19 September 2020, D. A. Zhigila 685 (Holotype GSUH! , isotypes FHI! , K! ) .

Diagnosis. Tinnea gombea is most similar to T. barteri in branches being lax (2–5 in number), stems terete in cross-section, leaf blades minutely hairy on both sides, inflorescence racemose, calyx bladder-like and in ecological requirements; but differ in growth form being annual subshrub, to about 40 cm tall, branching pattern fastigiate (versus annual herb,> 50 cm tall, virgate in T. barteri ), leaf attachment alternate to 2-nate or subopposite, blade lanceolate, leaf apex acuminate in T. gombea (versus opposite, orbicular, mucronate in T. barteri ), inflorescence racemose, solitary flowers in leaf and bract axils, anthers with basal hairs (versus spikes to 2–3-cymes, on long terminal head, anthers glabrous in T. barteri ) and fruits dehiscent (versus indehiscent in T. barteri ) ( Table 3 ).

Description. Erect annual subshrub, 15–40 cm tall, main branches 1–4, lax, fastigiate branches, arising from a taproot system. Stems woolly, green to grey-green, sometimes purple tinged toward the upper portion, terete. Leaves alternate or subopposite to 2-nate, shortly (0.2–0.5 mm) petiolate to subsessile; blade narrowly ovate to lanceolate, 2–7 × 1.5–3 cm, straight or recurved, covered with dense indument on both adaxial and abaxial sides, veins conspicuous on the abaxial surface, inconspicuous at the adaxial surface, base obtuse, margins entire, apex acuminate. Inflorescences are long racemes; usually arranged unilaterally, flowers solitary and borne in bract axils, lax in the lower, clustered in the upper portion; bracts usually subtending flowers, leaf-like (but smaller, 1–2 × 1–1.5 cm wide), alternately arranged, blade ovate to lanceolate, recurved backward, woolly on both side, acuminate; peduncles ca. 0.5 mm long, tan. Flowers lilac to purplish grey; calyx two unequal pairs, 5–12 × 3–5 mm, upper lobes equal, short and rounded, lower lobes unequal, longer and rounded, densely woolly indument, membranous; corolla tube ca. 15 mm long, woolly; stamens 4, sessile to subsessile, in two unequal pairs, anthers yellowish, attached to the corolla tube by a tuft of woolly hairs; styles 10–12 mm long, recurved, with unequally bifid stigma. Fruits inflated and bladder-like, ovate to orbiculate, dorsally circular wings well-developed, ca. 10 × 8 mm including the wings, 10-veined, covered with woolly hairs, tan to greyish brown, dehisces into two valves on maturity, 1-seeded. Seeds ca. 5 mm in diameter, covered with long fluffy indument.

Etymology

Tinnea gombea is named after its type locality, Gombe State, Nigeria .

Phenology

Tinnea gombea flowers from August to September and fruiting between September and October.

Distribution and habitat

Tinnea gombea is endemic to the Sudanian savanna and is currently known from Gombe State ( Fig 3 ). Apparently, the species is uncommon within its area of occurrence in grasslands and woodlands of Sudanian savanna. Usually found on abandoned farmland together with various annual herbs and with perennial shrubs such as Spermacoce L. species, Oldenlandia corymbosa L., Eragrostis tremula Hochst. , Physalis angulata L. and Vernonia ambigua Kotschy & Peyr. It usually grows at an elevation of about 620 m above sea level.

Conservation assessments

Tinnea gombea is known from the type locality only. We recorded <100 mature individuals in each of the three subpopulations. We have made a concerted effort to sample the species from other potential localities within and around abandoned farmlands in the Sudan savanna but were unsuccessful. Therefore, further botanical surveys for possible localities for this species is recommended. At present, the area of occupancy (AOO) of 0.5 km 2 and an extent of occurrence (EOO) of 5.00 km 2 were estimated for the known subpopulations. We project a continuous decline in the AOO, EOO, number of subpopulations and number of mature individuals for T. gombea given the level of accelerated urbanization toward its area of occurrence. Further, flooding and agricultural activities (crop cultivation and overgrazing) are critical threats to this species. Hence, preliminarily, the red list status of Critically Endangered (CR; B1, B2 (b, c), C2 (a, b) and D) under the categories and criteria B–D of the IUCN [ 34] guideline is assigned to T. gombea .

Additional specimen examined

NIGERIA. Gombe State: Akko Local Government Area, in farmlands of the grassland Sudanian savanna, elevation 620 m, 10˚ 17’ 6.11"N, 11˚ 1’ 55.6"E, 10 October 2020, D. A. Zhigila 684 (GSUH!, FHI!, K!) .

Figures

Fig 2. Morphological features of Tinnea gombea. (A) Plant habit and habitat; (B–D) young branches bearing vegetative and reproductive features; (E) Older branch with mature leaves, bracts and fruits; (G) closer view of dried fruits and leaves; (H) closer view of the fluffy seed with a tuft of basal hairs. Photos by D.A. Zhigila. https://doi.org/10.1371/journal.pone.0280550.g002

Fig 3. Distribution map of Tinnea gombea (black solid circle). The map was generated using naijR package version 0.4.0 as implemented in R version 4.2.0. and is therefore for illustrative purposes only. https://doi.org/10.1371/journal.pone.0280550.g003