Ochna mchanga T.Shah, 2023

Shah, Toral, Mashimba, Fandey H., Suleiman, Haji. O., Mbailwa, Yahya S., Savolainen, Vincent, Larridon, Isabel & Darbyshire, Iain, 2023, A taxonomic revision of the ecologically important Ochna holstii (Ochnaceae) complex using molecular and morphological data, Plant Ecology and Evolution 156 (2), pp. 174-200 : 174

8. Ochna mchanga T.Shah sp. nov.

Figs 13 , 14

Type.

MOZAMBIQUE • Cabo Delgado, Ntukwe to Kisongore , pt 441; 10°36 ’24.84” S, 40°19 ’40.44” E; 95 m; 15 Nov. 2009; fl.; Luke 13822; holotype: K! [K000787156]; isotypes: EA!, LMA, P, MO .

Diagnosis.

This species resembles O. polyneura Gilg in its leaf shape and in the foliage generally drying blue-black, but it differs by having generally smaller leaves 2-8 cm long and 1-3.5 wide (vs 5-11.5 cm long and 1.5-4.5 cm wide in O. polyneura ), smaller petals 6-7 mm long (vs 6-15 mm long in O. polyneura ), a shorter inflorescence rachis of 6-15 mm long (vs 3-30 mm long in O. polyneura ) and by having grey-brown or sometimes whitish, rough, fissured and slightly peeling bark (vs grey-brown, or sandy-brown, corky and fissured bark in O. polyneura ). Ochna mchanga is only recorded from coastal forests of south-eastern Tanzania and north-eastern Mozambique, whilst O. polyneura is widespread in miombo woodlands of Tanzania, Malawi, and Zimbabwe.

Description.

Shrub or small tree, 1-9 m tall. Bark grey-brown sometimes appearing whitish, rough, often fissured and slightly peeling. Stems grey-white or brown; new young growth dusty brown, puberulous. Stipules pale brown, linear, deciduous 1-1.5 mm long. Leaves green, drying dark blue-black, thin, glabrous, oblanceolate to oblong or elliptic, 2-8 cm long, 1-3.5(-4) cm wide, leaf base cuneate to attenuate, obtuse to acute or sometimes attenuate at apex, margins densely but shallowly serrate; lateral veins 10-14, almost at right angles to midrib then curving upwards, tertiary vernation reticulate prominent on both sides, midrib raised above, flat below; petiole 0.5-4.5 mm long; leaf buds brown, imbricate, pubescent, 1-6 mm long. Flowers precocious, arranged in racemes with 6-11 flowers, or in fascicles with 5-7 flowers; rachis 6-15(-20) mm long; pedicels 1-3 cm long, articulated 1-5 m from base, puberulous when flowering, seemingly glabrous in fruit, drying blue-black. Sepals green, often drying blue-black, oblong, 5.5-7 mm long, 3-3.5 mm wide, turning red in fruit 5-10(-20) mm long, 4-5.5 mm wide. Petals yellow, obovate-round, clawed, 6-7 mm long, 5.5 mm wide. Anthers dehiscing by longitudinal slits, 1.5-2 mm long; filaments 2.5-5 mm long. Carpels 5; style capitate at apex, 4-6.5 mm long. Drupelets black, ovate-round, 5-8 mm long, 5-6 mm wide.

Distribution.

South-eastern Tanzania, north-eastern Mozambique (Fig. 14 ).

Habitat.

Coastal thicket, coastal dry forest, woodland, on sandy soil. Altitude: 65-828 m.

Phenology.

Flowering and fruiting November to February, which corresponds to the rainy season occurring between November and March.

Etymology.

The specific epithet is the Swahili word for sand. This is because this species is most often found growing on sand in thickets and dry forests along the coast.

Preliminary IUCN conservation assessment.

Ochna mchanga is known only from south-eastern Tanzania and north-eastern Mozambique, with an estimated EOO of 83,998 km2 and an AOO of 52 km2. Timberlake et al. (2011) and Darbyshire et al. (2020a) noted significant threats to the dry forests and thickets of the Rovuma centre of endemism, including the increasing threat of land clearance for agriculture and settlements. As the species has a restricted distribution, with an AOO less than 2000 km2, and is known from approximately seven locations and with a continuing decline in the area and extent of habitat, the species is assessed as Vulnerable under criterion B: VU B2ab(iii).

Additional material examined.

TANZANIA • Luwangino; fl.; 1953; Crosse-Upcott 21A; K [K001082503]. - Rufiji District • Selous Game Reserve ; fl.; 4 Oct. 1970; Rogers 1157; K [K001082501] • Selous Game Reserve , N of Nakilala Thicket; 8°41'S, 38°20'E; 350 m; fr.; 14 Dec. 1975; Vollesen 3082; EA, K [K001082498] • Selous Game Reserve , Malemba Thicket; 8°40'S, 38°25'E; 400 m; fl.; 11 Jan. 1977; Vollesen 4309; EA, K [K001082500]. - Mtwara District • Naliendele Forest Reserve ; 10°25 ’17” S, 40°08 ’04” E; 145 m; st.; 13 Jan. 2020; Shah TS 75; K [K001561915] • Naliendele Forest Reserve ; 10°25 ’23” S, 40°08 ’07” E; 151 m; st.; 13 Jan. 2020; Shah TS 76; K [K001561914]• Mtiniko/ Mneveta Forest Reserve ; 10°35 ’46” S, 39°55 ’06” E; 210 m; st.; 13 Jan. 2020; Shah TS 78; K [K001567194]. - Lindi District • Rondo plateau, Mchinjidi [Mchinjiri], Rondo Nature Reserve ; 10°08 ’31” S, 39°11 ’48” E; 828 m; st.; 16 Jan. 2020; Shah TS 84; K [K001561916] .

MOZAMBIQUE - Nampula Province • Districto de Mossuril, Reserva Florestal da Mecrusso de Matibare ; fr.; 17 Feb. 1984; Groenendijk 1145; K [K000072636, K001387771] . - Cabo Delgado Province • Macomia district, Quiterajo; 11°49 ’39.9” S, 40°20 ’27.9” E; 100 m; fr.; 29 Nov. 2008; Timberlake 5579; K [K000738316] • Palma district , 10 km NW of Palma; 10°40 ’27.3” S, 40°25 ’55.3” E; 65 m; fr.; 6 Dec. 2008; Timberlake 5624; K [K000738319] • Palma district , intersection of oil cutline 34 with the Palma to Quissungule road; 10°41 ’23” S, 40°19 ’32” E; 115 m; fl., 19 Nov. 2009; Clarke 135; K [K000787149] • Quiterajo, within Majambo Forest ; 11°52 ’05.2” S, 40°19 ’40.5” E; 90 m; fr.; 27 Nov. 2008; Crawford FC 261; K [K000738317] • Quiterajo, S edge of forest block; 11°45 ’56” S, 40°22 ’04” E; fr.; 27 Nov. 2008; Müller 4091; K [K000738313] .

Notes.

Ochna mchanga , previously mistaken as O. polyneura , is elucidated as a cryptic species based on molecular and morphological evidence. The species is notably different by having smaller leaves and smaller inflorescences, including shorter rachis, shorter length of the pedicels below the articulation point and smaller petals. Furthermore, its bark is greyish-brown and fissured, compared to the brown corky bark of O. polyneura. Additionally, the two species differ in their habitat and ecology. Ochna mchanga occurs in coastal dry forests of south-eastern Tanzania and north-eastern Mozambique (also known as the Rovuma centre of endemism) that are not fire-prone or arguably fire-intolerant, whereas O. polyneura occurs in miombo woodlands of east and southern Africa that undergo regular burning.

Figures

Figure 13. Illustration of Ochna mchanga. A. Habit. B. Bark on mature stem. C. Adaxial of a medium-sized leaf. D. Serration of leaf margin, adaxial. E. Leaf apex, adaxial. F. Flower after loss of petals (style absent). G - H. Inner surface of sepals. I. Inner surface of the petal. J. Stamen. K. Ovaries, style, and stigma. L. Side view of flower post pollination showing immature drupelets. M. Underside of flower with three developing drupelets and a few persistent filaments. N. Upper side of flower with four mature drupelets. A, C, D, E from Luke et al. 13822 (K); B, N from Timberlake et al. 5579 (K); F-K from Vollesen 4309 (K); L, M from Timberlake 5624 (K). Drawn by Andrew Brown.

Figure 14. Distribution map for Ochna mchanga in Tanzania and Mozambique.