Begonia mariannensis Wassh. & T. McClellan, 1995

Moonlight, P. W. & Jara-Muñoz, A., 2017, A revision and recircumscription of Begonia Section Pilderia including one new species, Phytotaxa 307 (1), pp. 1-22 : 16

5. Begonia mariannensis Wassh. & T. McClellan ( Fig. 5 ; Fig. 7e )

Brittonia , 47 (1): 21, fig. 1 (1995). Type : TRINIDAD AND TOBAGO. Trinidad, Northern Range Mts. , Marianne River next to the Arima-Blanchisseuse road, 17 June 1991, J. A. Endler s.n. (lectotype (here designated) US [US00433417]; isolectotype US [US00744158]) .

Plants caulescent, rhizomatous herbs, 15–45 cm high; stem repent, rooting at the nodes, flexuous, unbranched; internodes to 0.5 (–1) cm long and rhizomatous at the base of the stem, woody, to 0.4 cm thick, to 2 cm long and trailing towards the apex, to 0.2 cm thick, succulent, glabrous to sparsely villous, hairs to 1 mm; stipules persistent, lanceolate, 4–7 × 2–3 mm, apex acuminate, margins entire, aciliate. Leaves alternate, clustered towards the apex of the stem, 5 or fewer, basifixed; petioles 1.5–8 cm long, very-densely villous to moderately villous with age, hairs to 1 mm; lamina weakly-asymmetric at the base, straight, lanceolate, 5.5–12 × 1.5–4 cm, apex acuminate, base cuneate on both sides of the blade, acuspidate, margins entire to irregularly-dentate at the apex, teeth 0.5–1 mm long, densely ciliate, the upper surface even, green, sparsely glandular-pilose between the tertiary veins, the veins glabrous to sparsely glandular-pilose towards the petiolar insertion, the lower surface sparsely glandular-pilose between the tertiary veins, the veins moderately-densely glandular-pilose to densely glandular-pilose towards the petiolar insertion; venation pinnate, with three to five veins from the base, with 3–5 lateral veins on the widest side of the lamina, and 3–4 lateral veins on the narrow side. Inflorescences: axillary, terminal, erect, 10–35 cm, densely glandular-villous throughout, thyrsoid with 3 to 10 lateral branches, basal-most lateral branch thyrsoid with ca. 3 lateral branches, lateral branches cymose, branching 1 to 3 times, protandrous; peduncle to 19 cm long, internodes to 5 cm long, decreasing to ca. 5 mm long at the apex, peduncles of cymes 5–20 mm; bracts tardily-deciduous, bracts of thyrsoid lateral branches like the leaves, the remainder ovate, 1–6 × 0.5–3 mm, membranous, glabrous, apex obtuse, margin entire to lacerate, ciliate; pedicels of male flowers 4–6 mm long, fibrous; pedicels of female flowers 4–8 mm long, fibrous. Male flowers: tepals 4, sparsely pilose outside, glabrous inside, margins entire, aciliate, the outer ovate, 5–7 × 3–4 mm, white, apex rounded, the inner linear, 1–4 × 0.5–1. 5 mm, white, apex acute rounded; stamens 10–15, united along the length of a 0.2–0.5 mm long column, yellow; filaments <0.4 mm, anthers linear, 0.2 × 0.1 mm, obtuse, dehiscing through lateral slits, the connective not projecting. Female flowers: bracteoles 3, persistent, ovate, 3–4 × 2–4, membranous, pilose, margins entire to lacerate, densely glandular-ciliate; tepals 5, persistent in fruit, subequal, lanceolate, 4–6 × 1–2.5, margins entire, aciliate; ovary body globose, 2.5–3.5 × 2–3.5 mm, densely glandular-pilose, 3-locular, unequally 3-winged, the wings sparsely glandular-pilose, largest wing triangular, ascending, widest 1/3 of the length towards the apex, 5–11 × 3–5 mm, the apex rounded, base cordate, the upper margin entire, ciliate, the lower margin lacerate, ciliate; the smallest 2 marginiform to triangular, not-ascending, 0.5–2 × 2–4 mm, apex rounded; placentae axile, bilamellate, ovuliferous all over; styles 3, 1.5–2 mm long, bifid 0.75 mm from base, the branches recurved, spirally twisted one time, persistent in fruit. Fruiting pedicel elongating to 12 mm. Fruit ovate, enlarging to 4 × 4 mm, largest wing the same shape as in the ovary, enlarging to 18 × 7 mm, the smallest enlarging to a triangular wing 5 × 5 mm. Seeds globose, 0.2 × 0.2 mm.

Distribution and habitat:— Trinidad and Tobago. Begonia mariannensis is only known from the Marianne and Yarra rivers on the northern slope of the Northern Range of Trinidad. The species is described as growing in the shade of evergreen forest on riverside rocks.

Taxonomic notes:— Begonia mariannensis was included in B. sect. Begoniastrum by its authors due to its bilamellate placentae; three, bipartite stigmas; and 4 and 5 male and female perianth parts respectively. Doorenbos et al. doubtfully included the species in B. sect. Knesebeckia , but with no explanation given. B. mariannensis possesses the glandular indumentum and thyrsoid inflorescences characteristic of the newly recircumscribed B. sect. Pilderia , however, and all the characters discussed by its authors are shared with species within the section.

Despite its straight, weakly-asymmetric, lanceolate and pinnately veined leaves, which are shared with B. buddleiifolia and B. tepuiensis , B. mariannensis appears most-closely related to B. glandulifera , with which it cooccurs. The two species form a clade with very little sequence divergence in our phylogenetic analysis and share with B. jenmanii their bipartite placentae and have similar upper leaf indumenta. B. mariannensis is easily distinguished from all other species in the section by its even (non-bullate), straight leaves.

IUCN Redlist Assessment:— Begonia mariannensis has an known AOO and EOO of> 10 km 2, the majority of which occurs outside protected areas. No information is available on population trends. An IUCN Red List category of Vulnerable (VU D2) is appropriate.

Additional specimens examined:— TRINIDAD: Yarra River , ca. 1.5km upriver, river bank, on rocks, 17 April 2004, W. Johnson & D. Jaggernauth s.n. ( BM) ; Marianne River , March 1987, V. Rush (paratype US [ US 00744162]) .

Figures

FIGURE 5. Begonia mariannensis Wassh. & T. McClellan. A. Habit; B. Male flower (front view); C. Female flower and branch of inflorescence (side view); D. Female flower (side view); E. Group of styles and stigmas (side view); F. Seeds. Reproduced from (Wasshausen & McClellan 1995) with the permission of Brittonia.

FIGURE 7. Distributions of species in Begonia sect. Pilderia (Klotzsch) A.DC. A. B. buddleiifolia A.DC.; B. B. glandulifera Griseb.; C. B. humillima L.B.Sm. & Wassh.; D. B. jenmanii Tutin; E. B. mariannensis Wassh. & T.McClellan; F.B. tepuiensis Moonlight & Jara.