Palisota stevartii Burg & E. Bidault 2019, spec. nova

8. Palisota stevartii Burg & E. Bidault, spec. nova (Fig. 15E–G, 16).

Holotypus: GABON. Prov. Ogooué-Lolo: concession CEB, NO de Bambidie, 00°40'48"S 12°48'51"E, 389 m, 17.XI.2015, fl., Stévart et al. 4842 (MO [MO-3047494]!; isotype: BRLU!, LBV!).

Palisota stevartii Burg & E. Bidault differs from all other Palisota species by the combination of leaves that are alternate below but form a terminal verticil, an erect, densely white woolly terminal inflorescence, up-curved bracts, and white flowers with indument, borne on very long pedicels extending out of the inflorescence.

Erect or decumbent herb ± 30 cm tall, occasionally to 80 cm, sometimes rooting at nodes, branched, or several stems emerging from the same base; roots fibrous. Stems green to reddish in vivo, sericeous with white to rusty trichomes ± 1– 2 cm long, more densely-velutinous on the nodes and sheaths, often glabrescent, internodes 3–10(–20) cm long, 3–7 mm in diam., brownish in sicco. Leaves alternate below, (2–)3–5(–6) in a terminal verticil; pseudopetioles hardly sheathing, the obscure sheath open for a quarter to a third of its length, occasionally to its base; pseudopetiole 0–2.5(–3.5) cm long; sheaths and pseudopetiole densely covered by erect, white to rusty trichomes 6 mm long; lamina elliptic to slightly obovate, (9–)15–20(–35) × (3–)5.5–9(–11.5) cm, base acute to obtuse, margins entire, with small, appressed, white or gingercoloured trichomes, apex abruptly acuminate, adaxial surface glossy, sparsely pubescent with white or rusty, erect trichomes, abaxial surface sparsely brownish pubescent, especially on the primary vein. Inflorescences strictly terminal, 1 per apical verticil, erect, spiciform, spiciform thyrse (3–)8–13(–18) × 1.5 –2.5(–4) cm, entirely covered by long, woolly, white, glutinous trichomes, including the flowers; peduncle 1–3.5(–12) cm long, very short at first, then expanding fully towards anthesis, all parts white, with 1–2 persistent, peduncular, leaf-like bracts, sheathing, acuminate, green to white, ± 2.5–7(–13) cm long, with whitish or pale green indument; floral bracts lanceolate to linear, 10–12(–18) × 2–3 mm, exceeding the length of buds, each subtending a cincinnus, persistent, white to pale green; cincinni ± 5 mm long, with ± 11–17 flowers, anthesis sequential, most cincinni generally bearing an open flower at the same time, buds oriented downward before anthesis. Flowers bisexual, white at anthesis, 8–10 mm in diam., pedicel expanding to 6–10 mm and spread at anthesis, exceeding the bract. Sepals equal, oblong-elliptic, 4.5–5 × 0.8–1.2 mm. Petals equal, similar to sepals, glabrous. Staminodes 3, subequal, filaments with long, yellow, spreading trichomes, the two lower ones 3 mm long, the upper one 4 mm long, antherodes lacking. Stamens 3, unequal, erect, the two upper ones with a filament 2.5–3 mm long, glabrous, anthers flattened, ellipsoid, slightly curved, 0.5 – 0.7 mm long, basifixed, yellow, often with a darker, reddish connective; the lower stamen with a filament 4–4.5 mm long, glabrous, anther thicker than the two upper ones, oblong, ± 0.75 mm long, folded at the apex, dorsifixed, white, with a dark reddish point of attachment to the filament. Ovary spherical, ± 1 mm in diam., with stiff trichomes 1.5 mm long, style 1.5–2 mm long, stigma shortly setaceous. Fruits not seen.

Etymology. – This species is named in honor of Dr. Tariq Stévart, who collected the type specimen and who has contributed to our knowledge of Palisota in Gabon by making numerous collections over the years. Tariq is also acknowledged for his important contribution to the study and conservation of the flora of Tropical Africa, in particular Orchidaceae.

Distribution and ecology. – Palisota stevartii appears to be endemic to Gabon, where it is known only from the eastern part of the country in Ogooué-Ivindo and Ogooué-Lolo provinces (Fig. 12). It grows in the understory of mature to secondary terra firme forests on slopes or plateaus. It is known from 250 to 705 m elevation.

Conservation status. – The EOO is 7,285 km ², within the range for “Vulnerable” status under Criterion B1, and the AOO is estimated at 28 km ², within the range for “Endangered” status under Criterion B2. Palisota stevartii is known from 7 collections, representing 6 sub-populations, one of which is situated in the Parc National d’Ivindo (Gabon). None of these sub-populations are thought to have been extirpated, given the recent collection dates and the fact that there is still significant forest coverage, including in the area where the oldest collection was made. Three sub-populations occur in logging concessions, including the SIAEFG concession located East of Birougou NP. The 6 sub-populations represent 6 locations with respect to the most important threat (forestry). This species is threatened by forest exploitation, which is projected to lead to future degradation of the quality of its habitat. Palisota stevartii therefore qualifies as “Vulnerable” [VU B1ab(iii)+2ab(iii)] according to the IUCN Red List Categories and Criteria (IUCN, 2012).

Notes. – Palisota stevartii resembles the other species with a decumbent habit and terminal inflorescences with numerous flowers forming a thyrse, either elongated or subglobose, such as P. fadenii, P. preussiana, as well as an undescribed new species being recognized by R.B. Faden that we have included in the key presented in this paper. While all of these species share the characteristics listed above, they show a great deal of variation in inflorescence morphology. Palisota stevartii is distinctive in that it has an elongated thyrse completely covered by a white woolly indument, which is unique in the genus. The fruits of two other species belonging to this group are red, almost spherical berries, differing from species in the group with shortly creeping stems as well as some rosette species, which are characterized by elongated and acuminate berries. However, the fruits of both P. stevartii and P. preussiana are yet to be observed so they may or may not conform to this pattern.

Paratypi. – GABON. Prov. Ogooué-Ivindo: Ivindo NP, Bai de Langoué, 00°10'23"S 12°31'49"E, 581 m, 11.XII.2016, fl., Texier & Bissiemou 282 (BRLU, LBV, MO, P, WAG). Prov. Ogooué-Lolo: c. 30 km E of Lastoursville, 00°50'00"S 13°00'00"E, 300 m, 19.XI.1993, fl., Breteler & Breteler 12192 (LBV, MO, WAG); Lastourville, Concession Forestière de la Compagnie Equatoriale du Bois, 00°48'46"S 13°13'06"E, 280 m, 3.XII.2012, fl., Ikabanga & Haurez 347 (BR, BRLU, LBV, MO); chantiers SBL, fin de rte 1, 20 km from Lastoursville Railway Bridge, 00°49'59"S 12°55'00"E, 250 m, 25.XI.1988, fl., Maesen et al. 5833 (WAG); Monts Birougou, Ramsar area, Maranda I village, 20 km S of Pana, 01°46'02"S 12°37'04"E, 705 m, 5.XII.2017, fl., Texier et al. 1433 (BR, BRLU, LBV, MO, P, WAG); SIAEFG logging concession, 30 km north of Pana, Monts Birougou, Ramsar area, 01°29'29"S 12°30'48"E, 705 m, 12.XII.2017, fl., Texier et al. 1648 (LBV, MO).