Grangea ogoouensis O. Lachenaud & Beentje, 2020

Beentje, Henk & Lachenaud, Olivier, 2020, The inclusion of Akeassia in Grangea (Asteraceae) and description of a new species from Gabon: Grangea ogoouensis, Candollea 75 (2), pp. 311-319 : 315-316

Grangea ogoouensis O. Lachenaud & Beentje , sp. nov.

( Fig. 1 , 2 ).

Holotypus: GABON. Moyen-Ogooué: Lac Onangué, 22.X.2014, Bidault et al. 1822 ( BR [ BR0000016174702 ]!; iso-: BRLU!, LBV!, MO!, P [ P00854719 ]!, WAG!).

Grangea ogoouensis O. Lachenaud & Beentje is closest to G. grangeoides (J.-P. Lebrun & Stork) Beentje & O. Lachenaud but differs by its mostly pinnatif id leaves (vs. leaves all shallowly toothed), larger phyllaries 1.2 –2.5 × 0.5 –1.2 mm (vs. 1.2 –1.5(–2) × 0.3 –0.4 mm) and fewer pappus bristles, 6 –16 in outer florets and 12 –18 in inner florets (vs. 0 –3(–5) and 4–9(–12), respectively). It also resembles G. maderaspatana (L.) Desf., but differs from this species by its pappus with free bristles (vs. pappus a coroniform ring), smaller phyllaries 1.2 –2.5 mm long (vs. 3 –7 mm long) and capitula mostly terminal and in groups of 2–5 (vs. mostly solitary and axillary).

Annual herb, clambering or erect, 5 – 40 cm tall; stem branched from near base, hispid-pubescent with multicellular hairs to 1 mm. Leaves obovate in outline, 15–50(–100) × 5–23(–54) mm, mostly lyrately pinnatilobed to pinnatifid (deepest and to 12 mm in proximal part, the lobes dentate) but the upper ones more shallowly dentate, base long-attenuate but the very base slightly widened and clasping the stem; apex mucronate-acute; sparsely hispid-pilose, more densely so near margins. Capitula solitary and stalked in upper leaf axils, or more commonly in groups of 2–5 near stem apex (the whole may look like a several-headed cyme when leaves are closely set); peduncle or stalk 1–5 mm long; capitula 2.5–4.5 mm high, 4– 7 mm in diameter; phyllaries 22– 24 in number, in 2 rows, 1.2 –2.5 × 0.5– 1.2 mm, pilose and pectinate to ciliate; receptacle convex, domed. Florets many (50+), corollas yellow; outer florets female, in 1–3 rows, cylindrical to narrowly infundibuliform, corolla 0.8–1.1 mm long, with a few trichomes (but no glands), (3–)4-lobed, lobes 0.15–0.3 mm long; inner florets many, bisexual, funnel-shaped, corolla 0.8–1.3 mm long, of which the lobes 0.2–0.3 mm, with a few hairs (and sometimes a few glands). Achenes 3-angular or (?when young) flattened, 0.8–1.2 mm long, slightly pilose, with a few glands; the outer with caducous pappus of 6–16 bristles 0.2– 0.3 mm long; the inner with pappus of 12– 18 slightly broad-based bristles 0.3–0.6 mm long.

Uses. – The plant sap is used to treat sinusitis (Quiroz-Villareal et al. 1523).

Distribution and ecology. – This species is endemic to west-central Gabon, where it is mostly found in the lower Ogooué basin ( Fig. 3 ). It occurs in ephemeral vegetation on seasonally flooded rocky or sandy banks of rivers and lakes, 10–106 m in elevation, and is locally common in this habitat, in association with other annual herbs such as Oldenlandia capensis L.f. and Pentodon pentandrus (Schumach. & Thonn.) Vatke (Rubiaceae) , Melochia corchorifolia L. ( Malvaceae ) and Euploca katangensis (Gürke ex De Wild.) E.L.A.N. Simons & Wieringa (Boraginaceae) . It has been collected in flower from March to May and from August to October, corresponding to periods of moderate water levels.

Conservation status. – The extent of occurrence of Grangea ogoouensis is estimated to be 25177 km ², above the limit for Vulnerable status under criterion B1, and its area of occupancy to be 44 km ², within the limit for Endangered under criterion B2. The species is endemic to Gabon and occurs in ephemeral vegetation along lakes and rivers, mostly in the Ogooué river system. It is known from 13 specimens representing 11 occurrences, only one of which occurs in a protected area (Lopé National Park). One occurrence is in a mining concession (Mabounié) where its habitat is at risk from the building of infrastructure associated with mining activities, and another in an oil concession (near Rabi) where similar disturbance is expected due to oil exploitation. Furthermore, there are projects to dredge the Ogooué river between Lambaréné and Port-Gentil to facilitate navigation, which would seriously affect the water regime and consequently the habitat of the species. For all these reasons, a decline in habitat extent and quality and number of mature individuals is projected. The 11 occurrences represent eight locations in the sense of IUCN (2019) – all occurrences on the Ogooué downstream of Lambaréné being treated as a single location since they are at risk from the same event – and the species thus qualifies for “Vulnerable” [VU B1ab(iii,v)+B2ab(iii,v)] using the IUCN Red List Categories and Criteria ( IUCN, 2012).

Notes. – The earliest collections of this species were cited as Akeassia grangeoides by LEBRUN & STORK (1993); see the note under G. grangeoides . The plant illustrated as G. maderaspatana in WHITE & ABERNETHY (1996: 21, fig. a) is presumably G. ogoouensis .

Grangea ogoouensis is, as far as known, the only species of Asteraceae endemic to Gabon. SOSEF et al. (2006) record Erlangea plumosa Sch. Bip. as endemic to the country, but this species also occurs in the Republic of Congo.

Paratypi. – GABON. Moyen-Ogooué: env. village Olamba, 9.VIII.2011, Boupoya et al. 461 ( BRLU, WAG) ; Lambaréné, 21.III.1989, Bourobou 55 ( LBV) ; Ogooué river 3–4 km downstream from Ndjolé , 28.IX.1994, Breteler & Breteler 13066 ( BR, LBV, WAG) ; Mabounié, 10.V.2012, Stévart & Boupoya 4501 ( BRLU, LBV, MO) ; env. de Lambaréné, sur l’Ogooué, 1.VIII.1912, Fleury in Chevalier 26242 ( P) ; Ndjolé, banks of now very low Ogooué , 4.IX.1992, Wieringa & van de Poll 1585 ( LBV, WAG). Ogooué-Ivindo: Booué, 26.VIII.1957, Anton-Smith 278 ( P) ; Lopé, en-dessous du pont sur l’Ogooué , 0°06'17"S 11°24'56"E, 9.III.2010, Bissiengou et al. 1088 ( LBV, WAG) ; PN de la Lopé , gallery forest of the Ogooué river , 0°05'02"S 11°36'43"E, 1.IX.2012, Quiroz-Villarreal et al. 1523 ( WAG) ; Lopé, Ogooué-Airstrip beach , 29.VIII.1993, L. White 1019 ( LBV). Ogooué-Maritime: M’Paga (or M’Paya), banks of Ogooué , 12.IV.1986, Pauly 257 ( BR) ; near Echira oilfield , 30.IX.1994, Wieringa & Nzabi 2817 ( BR, LBV, P, WAG).

Figures

Fig. 1. – Grangea ogoouensis O. Lachenaud & Beentje. A. Entire plant in habitat; B. Capitula and upper leaves; C. Capitula. [Bidault et al. 1822] [Photos: E. Bidault]

Fig. 2. – Grangea ogoouensis O. Lachenaud & Beentje. A. Plant in flower; B. Basal leaf; C. Upper leaf; D. Capitula; E. Outer phyllary; F. Inner phyllary; G. Outer (female) floret; H. Inner (hermaphrodite) floret. [Bidault et al. 1822, BR] [Drawing: O. Lachenaud]

Fig. 3. – Distribution map of Grangea ogoouensis O. Lachenaud & Beentje.