Mcvaughia

Shrubs to subshrubs, perennial, growing in sandy soils. Branches cylindrical, densely sericeous or lanate-velutinous, generally glabrescent at age. Stipules epipetiolar, completely connate, persistent. Leaves opposite; petiole eglandular; blade bearing 2–many glands abaxially. Thyrsi terminal, pedunculate, many-branched; cincinni alternate to subopposite, 1–14-flowered; bracts persistent; bracteoles persistent, one of them 1-glandular, the other eglandular, gland green in bud turning yellow in anthesis. Flowers zygomorphic; floral buds slightly flattened at middle; pedicel stout, straight in bud. Sepals leaving petals exposed in pre-anthesis, all 2-glandular. Petals bright to golden yellow, glabrous, the anterior two remaining cupped one inside the other; lateral petals with the margin erose; posterior petal bearing several marginal glands. Stamens 7–8, staminodes 2–3 (stamens opposite the posterior-lateral sepals and the posterior petal); filaments glabrous, those opposite the posterior-lateral petals slightly curved towards the apex; connectives inconspicuous; anthers horseshoe-shaped, glabrous, outer locules confluent at apex, reduced to antherodes in staminodes. Ovary 3-carpellate, 3-locular, 2 locules ± anterior, apparently collapsed lacking ovules, 1 locule almost posterior, fertile, 1-ovulate; styles 3, slender, truncate to uncinate at apex; stigma minute, lateral. Drupes rugose, twisted, asymmetric, 1-locular, proximal chamber thick-walled, 1-seeded, distal chamber thin-walled, filled with a viscous secretion (allowing the fruit to float and to be dispersed by water).

Mcvaughia is restricted to sandy soils within sedimentary basins of Northeastern Brazil, with different species being endemic to each sedimentary basin: Mcvaughiabahiana – Tucano basin, M.piauhiensis – Parnaiba basin, and M.sergipana – Sergipe-Alagoas basin (Amorim and Almeida 2015). Sedimentary basins represent conspicuous phytogeographic zones within the Caatinga domain, with a distinct biota from other areas of Caatinga over crystalline shield, holding endemism records for some angiosperm families (Cardoso and Queiroz 2007; Almeida et al. 2018; Silva and Souza 2018).