Memecylon nubigenum R.D. Stone & I.G. Mona, 2017

Stone, Robert Douglas, Mona, Imercia Gracious & Ramdhani, Syd, 2017, Revised treatment of Mozambican Memecylon (Melastomataceae-Olisbeoideae), with descriptions of four new species in M. section Buxifolia, Phytotaxa 331 (2), pp. 151-168 : 158-160

Memecylon nubigenum R.D. Stone & I.G. Mona , sp. nov. ( Fig. 4 )

Type:— MOZAMBIQUE. Prov. Nampula: Ribáuè, serra Mepáluè, elevation ca. 1600 m, 09 December 1967, Torre & Correia 16431 (holotype LISC!, isotypes COI, K!, LMU!, PRE!, SRGH).

Evergreen understory tree 4–7 (–17) m tall. Youngest branchlets brown to dark brown, strongly quadrangular and ± narrowly alate; older branchlets eventually becoming terete, grayish brown to grayish white, ± longitudinally fissured; nodes thickened; internodes (1–) 1.8–3.2 (–4.5) cm long. Leaves subcoriaceous, dark green on the upper surface, paler beneath; petioles 1–3 (–4) mm long; blades ovate, varying to ± elliptic, (2.5–) 3.5–5 (–6) × (1.2–) 1.8–2.5 (–3.2) cm, cuneate to rounded at base, ± broadly acuminate at apex, the acumen up to 8 mm long, obtuse varying to rather acute or sometimes indistinct, margins narrowly and shallowly revolute; midnerve clearly visible, impressed on the upper surface, prominent on the lower (especially toward the leaf base); intramarginal nerves faintly visible on the upper surface; transverse veins 4–5 pairs, oriented at an oblique angle relative to the midnerve, obscure or ± faintly visible on the upper surface in dried material. Cymes ca. 1.5 cm long, 1–3-flowered, solitary to geminate or in fascicles of 2, borne at the defoliated nodes of older branchlets, in the leaf axils and at the bracteate nodes alternating with those bearing fully developed leaves; peduncles 1–7 (–11) mm long; secondary axes 1–6 mm long; bracts rapidly deciduous. Flowers borne individually at the ends of the inflorescence axes, on pedicels 1–3.5 mm long; hypantho-calyx ca. 2.5 mm high × 3.75 mm wide, obconic; lobes broadly rounded, ca. 0.5 × 2 mm, green and subcoriaceous with a very narrow scarious margin; corolla in bud distinctly apiculate, subacute at apex; petals white, subrhombic, 5 × 4 mm, acute at the apex; staminal filaments ca. 6 mm long; anthers ca. 2.5 mm long, connective strongly incurved by the dorsal oil-gland; ovules 2–8; style 10 mm long. Fruits baccate, 1-seeded, green becoming black at maturity, subglobose, 7–8 mm high × 7–8 mm in diameter, crowned by the persistent calyx ca. 1 mm high; epigynous chamber lacking radial partitions, marked only by the scars of the deciduous petals, anthers and style.

Additional specimens examined (paratypes):— MALAWI. Southern Region: Mlanje District, Ruo Gorge , elevation ± 1000 m, 01 September 1970, Müller 1474 ( COI, K!, SRGH) ; Mulanje District, Ruo Gorge 2.5 km above Hydro Electric Station [ S side of Mulanje Mt.], elevation 1250 m, 07 May 1980, Blackmore et al. 1512 ( K!, MAL) ; Mulanje Mt. District, Lichenya Forest ( Mim-Mim path), elevation 1820 m, 29 September 1983, Dowsett-Lemaire 1026 ( BR!) ; Mulanje Mt. District, Great Ruo Gorge , elevation 1250 m, 23 June 1984, Dowsett-Lemaire 1159 ( BR!) ; Mt. Mulanje, Pamba Gorge at Savani stream crossing, elevation 1250 m, 30 September 1986, Chapman 8098 ( K!, MO!, PRE!) ; Mt. Mulanje, Chisongeli Forest ( West ), elevation 1500 m, 15 September 1988, Chapman 9292 ( K!, MO!, PRE!, WAG!) ; Mulanje District, Lujeri Power Station, above Lujeri Dam, along Ruo River , elevation 1137 m, 15°57'16.15"S, 35°11'16.83"E, 13 July 2007, Nothale & Patel 171 ( K!) . MOZAMBIQUE. Prov. Zambézia: Guruè, encosta da serra do Guruè via fábrica Junqueiro a Oeste dos Picos Namúli, próx. do rio Malema , elevation ca. 1700 m, 06 November 1967, Torre & Correia 15956 ( COI, EA, K!, LISC, SRGH) .

Distribution and habitat: —Known from two granitic inselbergs in northern Mozambique, i.e., the Namúli massif (Zambézia Province) and Monte Mepáluè (Nampula Province), in cloud forest at 1600–1700 m elevation ( Fig. 3 ). The collecting localities of Torre and Correia in November 1967 were on the eastern side of the Namúli massif, on slopes and in riverine forests of Mt Namúli ( Timberlake et al. 2009: 24).

Also known from the Mulanje massif, a granitic inselberg in southern Malawi, at elevations of 1000–1800 m, in forests classified as either “mid-altitude” or “submontane” ( Dowsett-Lemaire 1988, 1989). At Mulanje, most collections of M. nubigenum are from the Ruo Gorge at the southern end of the massif, with other forested localities represented by single collections (Lichenya Plateau, Chisongeli, Pamba Gorge).

Phenology: —Flowers in December. Fruiting collections in May–July, also in September and November.

Conservation status: — Memecylon nubigenum is known from six locations including two in northern Mozambique and four in southern Malawi (Mulanje massif). It has an EOO of ca. 5,900 km 2 and an AOO of 24 km 2 (assuming a 4 km 2 grid cell size).

In Mozambique, the type locality in Nampula Province is formally protected in the Mepáluè [M’páluè] Forest Reserve which has a reported area of 42.5 km 2 ( Faye 2005). At the base of the mountain, the village of Ribáuè lies in a densely populated valley. Natural vegetation on the lower slopes has already been converted to subsistence agriculture, but human intrusion at the higher elevations (above 1100 m) is impeded by steep slopes and lack of road access ( Müller et al. 2005). The second Mozambican location, in the Namúli massif near Guruè (Zambézia Province), is not formally protected but has been recommended for such status ( Timberlake et al. 2009). Much of the natural vegetation below 1500 m elevation has already been transformed, but ca. 10 km 2 was covered by montane forest at elevations of 1600–1900 m (determined from 2005 Landsat imagery). Major threats in forested habitats above 1400 m include potato cultivation, frequent wildfires, and logging.

The locations in Malawi are protected in the Mulanje Mountain Forest Reserve, first gazetted in 1927 but with later boundary adjustments due to on-going human encroachment on the lower slopes. The massif is surrounded by villages of the Mulanje and Phalombe districts, tea estates, and small-scale cultivation. According to Dowsett-Lemaire (1988), forest cover (estimated from aerial photographs) was 15 km 2 at middle elevations (900–1500 m) and 46 km 2 on the upper slopes and plateaux (1500–2300 m). Continuing threats include clearing of forest for subsistence agriculture and charcoal production, wildfires, extraction of the commercially valuable Mulanje cypress ( Widdringtonia whytei Rendle ), and spread of the naturalized Mexican weeping pine ( Pinus patula Schiede ex Schltdl. & Cham. ). Deforestation has been most severe on the southern and southeastern slopes of the massif, in or near areas where M. nubigenum has been collected in the past, i.e., Chisongeli and near the entrance to the Ruo Gorge ( Dowsett-Lemaire 1988). This trend of environmental deterioration and unsustainable resource exploitation led to the establishment of the non-governmental Mulanje Mountain Conservation Trust around 1994. This organization has attracted substantial funding from the World Bank (2001–2008) and more recently the Norwegian government ( Wisborg & Jumbe 2010).

Memecylon nubigenum is thus provisionally assessed as Vulnerable [VU B1ab(iii)+B2ab(iii); D2] according to the IUCN Red List Categories and Criteria ( IUCN 2012).

Etymology: —The epithet nubigenum is a compound derived from the Latin noun nubis meaning “cloud” and the verb gignere meaning “to be born.” It functions as an adjective and means “born of or originating from the clouds.” It is a reference to the habitat in mountains of northern Mozambique and southern Malawi.

Discussion: —The Memecylon populations from mountains of northern Mozambique and southern Malawi (Mt Mulanje), described herein as M. nubigenum , were earlier identified as M. natalense ( Fernandes & Fernandes 1972, 1978, 1980) but are evidently not very closely related to that species (Stone et al. 2017), clearly indicating the need to recognise them as a distinct taxon. Memecylon nubigenum also differs morphologically from South African M. natalense sensu stricto in the shape of the leaf apex (mostly obtuse in M. nubigenum vs acute in M. natalense ), the shape of the corolla in bud (distinctly apiculate vs rounded to subacute), and the shape of the fruits (strictly globose vs ± ellipsoid or tending to be somewhat longer than wide) ( Table 1).

The new species was previously illustrated by Fernandes & Fernandes (1972: tab. 2, as M. natalense ).

Figures

FIGURE 3. Distribution of species of Memecylon section Buxifolia in Mozambique and adjacent parts of Malawi and Tanzania: M. incisilobum (black star); M. nubigenum (black triangles); M. rovumense (black circles); M. aenigmaticum (open diamond). Political boundaries are indicated by solid lines, and selected cities by open squares.

FIGURE 4. Memecylon nubigenum. Image of the holotype (Torre & Correia 16431, LISC). Source: Herbario, Instituto de Investigação Científica Tropical, Museu Nacional de História Natural e da Ciência, Universidade de Lisboa, Portugal.