Benna alternifolia Burgt & Ver.-Lib., 2022

van der Burgt, Xander M., Haba, Pepe M., Magassouba, Sékou & Veranso-Libalah, Marie Claire, 2022, Benna alternifolia (Melastomataceae: Sonerileae), a new herbaceous genus and species from Guinea, West Africa, Willdenowia 52 (1), pp. 25-37 : 31-35

Benna alternifolia Burgt & Ver.-Lib. , sp. nov. – Fig. 2 , 3 , 4 .

Holotype: Guinea, Forécariah Prefecture, slopes of Benna Plateau , 3 km W of Gombokori village , 09°44'06"N, 12°49'00"W, 770 m, flower buds, 11 Feb 2019, Burgt, Haba, Konomou & Xanthos 2274 ( HNG; isotypes: K001381567 , MO, P, WAG) .

Description — Herbs, perennial, evergreen, half-spherical in shape, up to 1.2 m in diam., with up to 60 leaves per plant. Roots woody; thin roots up to 0.5 m × 4 mm, radiating on rock surface and attaching plant to rock; thick roots up to 10 m × 2 cm, entering rock fissures in search of permanent water seepage, bark deeply fissured, up to 5 mm thick. Stems somewhat woody, branched from base, pendent, circular in cross-section, up to 28 cm × 6–12 mm, reddish green, densely to sparsely hairy with red hairs up to 4 mm long, puberulent with red glandular hairs up to 0.1 mm long; internodes up to 3 cm long, leaf petiole pointing in same direction as internode just below it. Leaves alternate; petiole succulent, 15–45 cm × up to 6 mm, reddish green to bright red, densely hairy to glabrescent with red hairs up to 7 mm long, puberulent with red glandular hairs up to 0.1 mm long; leaf blade round to ovate, 12–31 × 10–28 cm, shrinking a little during drying, lower surface dull glaucous light green, upper surface glossy green, both surfaces puberulent with red glandular hairs up to 0.1 mm long, veins below with red hairs up to 5 mm long; leaf base deeply cordate, left or right half of leaf base often overlapping other half; leaf margin dentate, teeth with a single red hair up to 4 mm long, distance between teeth 4–24 mm; leaf apex rounded, mucronate; leaf venation acrodromous, 11–15 veins all starting from top of petiole, central vein straight, other veins curved, otherwise similar in appearance to primary vein, secondary and tertiary venation scalariform, venation on lower surface prominent, light red, on upper surface flattened, light red. Inflorescence cymose, paniculate, axillary, up to 4 cm long when in bud, with up to c. 70 flower buds, branching alternate; peduncle up to 1 × 3 mm, internodes 0.5–15 mm long; bracts and bracteole persistent, lanceolate, c. 1 mm long; peduncle and rachides red, puberulent with red glandular hairs up to 0.1 mm long. Flowers: flower buds 4-merous, epigynous; pedicel up to 24 mm long, red, puberulent with red glandular hairs up to 0.1 mm long; hypanthium cupuliform, c. 4 × 4 mm, light reddish green, puberulent with red glandular hairs up to 0.1 mm long, part of hypanthium free from ovary c. 2 mm long; calyx lobes 4, free, triangular, c. 1.5 × 2.5 mm, light green with pink apex, puberulent with red glandular hairs up to 0.2 mm long, margin ciliate, apex mucronate, mucro c. 0.3 mm long; petals 4, free, convolute, overlapping counterclockwise when viewed from above, alternate to sepals, round to ovate, in bud c. 6 × 5 mm, light pink, both surfaces and margin glabrous, acuminate with acumen c. 1 mm long, claw c. 0.5 × 1 mm; stamens 8, fertile, actinomorphic, dimorphic, glabrous; 4 antisepalous stamens: filaments c. 2 mm long, connective with a 3-lobed appendage, c. 2 × 2 mm, anther c. 3 × 1 mm, with 2 loculi; 4 antipetalous stamens: filaments c. 1 mm long, connective with a 3-lobed appendage, c. 1 × 1 mm, anther c. 2 × 1 mm, with 2 loculi; ovary inferior, in bud c. 2 mm long, 4-locular, loculi opposite sepals, each locule with c. 100 ovules; style straight, in bud c. 4 mm long, glabrous, stigma punctiform. Infructescence up to 9 cm long, with up to 70 fruits, peduncle up to 1 × 4 mm, internodes 0.5–18 mm long, lower internodes up to 2 mm long, middle internodes up to 18 mm long, upper internodes up to 5 mm long; bracts and bracteole caducous; peduncle and rachides red, puberulent with red glandular hairs up to 0.1 mm long. Fruit a capsule, urceolate, 4–5 × 3–4 mm, glabrescent, calyx persistent, fruit apically dehiscent, crown lobes not seen; fruit pedicel 20–60 mm long. Seeds up to 400 per fruit, obovoid or nearly so, 0.4–0.5 × 0.3–0.4 mm, glossy, testa smooth, yellow to light brown.

Phenology — Benna alternifolia flowers in February– March and fruits a few months later. Old, decaying fruits containing ripe seeds may remain on the plants until November, because the plants are little disturbed by wind and rain in their sheltered habitat. Distribution — Benna alternifolia is endemic to Guinea ( Fig. 5 ) and occurs in Forécariah Prefecture near border with Kindia Prefecture, in canyons of the Benna Plateau near villages Dalonia and Gombokori.

Habitat and ecology — Benna alternifolia occurs on vertical sandstone rock, in deep shade in canyons 10–100 m deep ( Fig. 3 ), and on vertical sandstone rock in deep shade of trees, at 300–800 m altitude. Plants occur only under overhanging rocks ( Fig 3B ), out of reach of falling rain drops, and only on vertical rock where water is seeping all year round, within reach of the several-meter-long roots. In this habitat, the perennial, evergreen, herbaceous plants, which do not have a rootstock, can continue to grow during the six-month dry season.

Benna alternifolia is often found together with Cincinnobotrys felicis ( A. Chev.) Jacq.-Fél. ( Melastomataceae ), Impatiens bennae ( Balsaminaceae ) and Mesanthemum bennae ( Eriocaulaceae ). On the same vertical rocks, but higher up and in sunny, seasonally dry habitat, two plant species endemic to Guinea occur abundantly: Cailliella praerupticola ( Melastomataceae ) and Pitcairnia feliciana ( Bromeliaceae ), the only member of the family that is native outside America.

Conservation status — Benna alternifolia is currently known only in the Benna Plateau in Forécariah Prefecture. The collectors searched for the species elsewhere in the region, without success. The habitat of the species was found to occur widespread in an expanse of sandstone plateaus occupying much of Coyah, Dubreka, Forécariah and Kindia Prefectures in Guinea ( Fig. 5 ), but the species was not found. The Benna Plateau is currently unprotected and was not proposed as a TIPA (Tropical Important Plant Area) by Couch & al. (2019), because the exact location of the Benna Plateau was unknown to the authors at the time of that publication. The Benna Plateau is rich in rare plant species and is proposed here to become a TIPA.

The extent of occurrence of Benna alternifolia was 3.4 km 2 and the area of occupancy was 12 km 2, both calculated with Geocat (2021). The extent of occurrence is changed to 12 km 2, because it should not be smaller than the area of occupancy ( IUCN 2019). The number of locations is two. These values may become larger if the species is found in other canyons. The species currently does not seem exposed to any threats. The habitat where the species occurs is free of fire. There are no known mineral deposits in the vicinity. Plants were only found in remote canyons where they will not be threatened by rock quarrying. In absence of any threats to the species, IUCN (2012) categories A, B and C are not eligible. About 680 mature individuals of B. alternifolia were found. There exist probably more than 1000 mature individuals, because some canyons in and near the Benna Plateau are yet to be explored. The species may be close to qualifying for the IUCN (2012) Red List category Vulnerable under criterion D1, which has a threshold of 1000 mature individuals, and B. alternifolia is therefore assessed here in the IUCN category Near Threatened.

Seed conservation — Seeds were collected from 12 plants of Burgt & Haba 2333 and are stored in the seed bank of the National Herbarium of Guinea in Conakry (c. 250 seeds) and at Kew’s Millennium Seed Bank (also c. 250 seeds).

Etymology — The genus is named for the Benna Plateau or Benna Gadyah in the Susu language. The Benna Plateau holds the only known locations for the species. The specific epithet refers to the alternate leaf arrangement.

Vernacular name — In the Susu language, the name of Benna alternifolia is Labalaba Khamè or Labalaba Hamey, which means “male soft leaf”. The name Labalaba is given to Piper umbellatum L. ( Burkill 1997, vol 4: p. 441), a herb with leaves similar in size and appearance. On the Benna Plateau , Piper umbellatum is named Labalaba Guinè, which means “female soft leaf”.

Additional specimens examined — GUINEA: Forécariah Prefecture, canyon at base of Benna Plateau , 3.5 km N of Dalonia village, 09°41'53"N, 12°50'03"W, 330 m, fruits, 26 Oct 2019, Burgt, Haba & Holt 2323 ( B, HNG, K, MO, P, WAG); slopes of Benna Plateau , 3.5 km W of Gombokori village, 09°44'07"N, 12°49'26"W, 810 m, fruits, 1 Nov 2019, Burgt & Haba 2333 ( HNG, K).

Figures

Fig. 2. Benna alternifolia – A: branch showing alternate leaf arrangement, with two inflorescences and seven leaves: five mature leaves of which three removed, a young leaf, and a very young leaf; B: flower bud; C: petal inner surface; D: flower bud in longitudinal section with petals partly removed; E: large stamen back and front, small stamen back and front; F: ovary of flower bud in transverse section; G: ovary of flower bud seen from above; H: old infructescence with fruits partly decomposed; J: fruit; K: seeds. – Origin: A from Burgt & al. 2274 (type gathering) and Burgt & al. 2323; B–G from Burgt & al. 2274; H–K from Burgt & Haba 2333. – Drawing by Xander van der Burgt.

Fig. 3. Benna alternifolia – A: the largest population was found in a deep canyon, of which the upper part is visible at the centre of the photograph, on a 1040 m-high hill on the Benna Plateau; B: plants in their habitat, on vertical rock in deep shade, under overhanging rocks, out of reach of falling rain drops, but within reach of permanently seeping water; C: group of four plants; D: single plant. – Origin: A, C from Burgt & al. 2274 (type gathering); B from Burgt & al. 2323; D from Burgt & Haba 2333. – All photographs by Xander van der Burgt.

Fig. 4. Benna alternifolia – A: leaf upper surface; B: leaf lower surface; C: inflorescence with flower buds; D: roots. – Origin:A, D from Burgt & Haba 2333; B, C from Burgt & al. 2274 (type gathering). – All photographs by Xander van der Burgt.

Fig. 5. Distribution of Benna alternifolia, blue dots. Map data © Google 2021.