Vitex zigzag Callm. & Phillipson, 2021

Callmander, Martin W. & Phillipson, Peter B., 2021, Towards a Revision of the Genus Vitex (Lamiaceae) in Madagascar. II: Three New Species from the Littoral Forests, Novon: A Journal for Botanical Nomenclature 29, pp. 38-47 : 44-46

3. Vitex zigzag Callm. & Phillipson , sp. nov.

TYPE: Madagascar. SAVA [Antsiranana]: Vohémar, forêt littorale sur sables d’Ambondrobe , 13°42′49″S 50°05′13″E, 5 m, 1 Mar. 2003, fl., J. Rabenantoandro, R. Rabevohitra, R. Razakamalala & Ismael 1402 (holotype, G [bc] G00341725! ; isotypes, MO-04803544! , P [bc] P04397710! , TAN n.v.). Figure 4 .

Diagnosis. Vitex zigzag Callm. & Phillipson differs from its congeners in Madagascar by the combination of its abaxial leaf surface covered by a very fine beige velutinous indument, its divaricating, 3- to 5-times branching dichasial inflorescence with a zigzag pattern with the terminal flower often missing, and its pale yellow corolla that is sericeous outside.

Tree up to 15 m tall. Young vegetative parts and inflorescence branches generally with a somewhat obscure puberulous, mid-brown indument. Leaves palmate, (2- to)3- to 5-foliolate; petiole 3–14 cm; leaflets obovate to oblanceolate, petiolulate (petiolule 0.3–1.5 mm), chartaceous, the largest (median) leaflet 5–15 × 2–4 cm; blade dark brown or grayish above and beige below in sicco; base attenuate; apex generally rounded, sometimes emarginate or acute, often finely apiculate; margin entire; abaxial surface covered by a very fine beige velutinous indument, with midrib prominent; adaxial surface glabrous, with midrib impressed. Inflorescence axillary (normally in opposite pairs), a widely divaricating, 3- to 5-times branching dichasium, with the terminal flower often missing, giving a zigzag aspect; peduncle 1–2.5 cm; branches ca. 1 cm, <1 mm diam.; flowers borne on 5–8-mm pedicels with a pair of small caducous bracteoles; pedicels elongating in fruit, with a very fine beige velutinous indument. Calyx narrowly campanulate, 6–7 × 3–4 mm, 5-lobed, lobes rounded, ca. 1.5 mm, covered by a similar indument to the pedicel. Corolla tubular, curved, ca. 15 × 4 mm, tapering to 1 mm diam. at base, pale yellow sericeous outside, purple to brown and glabrous inside (except the sericeous proximal part); lobes broadly triangular, ca. 1 × 2 mm. Stamens 4, curved, exserted by ca. 7 mm; filaments ca. 22 mm, the portion within the tube villous; anthers ca. 1 mm. Style ca. 22 mm, shortly bifid. Fruit a drupe, obovoidal, ca. 1 × 0.5 cm, wrinkled when dried, cupped by the accrescent calyx for ca. 1/2 its length.

Etymology. Vitex zigzag is named after the characteristic divaricate “zigzag” branching pattern of its inflorescences.

Distribution and ecology. Vitex zigzag is known only from two small patches of littoral forest in the SAVA Region of northeastern Madagascar from sea level to ca. 50 m. s.m. Two collections (Miller 4267 and Service Forestier 27708) probably represent a single subpopulation from “Ampandrozonana” south of Sambava adjacent to Sambava airport, probably in a small fragment of secondary peri-urban littoral forest. This remnant of coastal sand forest was dominated in 1989 by Afzelia Sm. (Fabaceae) and Barringtonia J. R. Forst. & G. Forst. (Lecythidaceae) , and the understory had mostly been cut and planted with vanilla (Miller 4267); but recent satellite imagery shows this area to have no signs of any remaining forest. The new species is most likely to have been extirpated from this location during the past 30 years. The second subpopulation is represented by four relatively recent collections from Ambondrobe Forest, situated ca. 60 km to the north of the first subpopulation and some 40 km south of Vohemar, where it was collected during Missouri Botanical Garden’s littoral forest inventory project ( Consiglio, 2006). This site, a narrow, isolated strip of unprotected littoral forest on sand approximately 9 km 2 in surface area, is believed to be still largely intact.

Conservation status. As stated above, Vitex zigzag probably only survives at a single site, Ambondrobe Forest, between the cities of Vohemar and Sambava. It is likely to have been present in other littoral forests in this area, such as around Sambava where it was previously recorded, but the demand for land for cultivation, notably for vanilla plantations, and for habitation has destroyed almost all littoral forests in this area of Madagascar. While Ambondrobe remains relatively intact, it is believed to have once been part of a much larger area of forest which has now been destroyed ( Consiglio, 2006), and it is likely only a matter of time before pressure on the remaining area causes loss of viable habitat and eventually destruction of the forest unless adequate conservation measures can be put in place.

The extent of occurrence (EOO) and the area of occupancy (AOO) of Vitex zigzag are both less than 10 km 2, and the range consists of a single known extant location. Continuing decline has been observed and can be inferred, and is also projected in terms of the species’ extent of occurrence, area of occupancy, and quality of habitat. We therefore assign a status of “Critically Endangered” [CR B1ab(iii)+B2ab(iii)] using the IUCN Red List Categories and Criteria ( IUCN, 2012).

Notes. Vitex zigzag is very distinctive among the Malagasy Vitex species and can be easily characterized by its divaricating, 3- to 5-times zigzag branching inflorescence.

Vitex zigzag is a rare and threatened species, and although it is adequately represented by herbarium specimens, a search for the species in any sites containing remnant littoral forest species between Vohemar and Sambava, even extending south from Sambava as far as the Lokoho River mouth, may reveal other sites at which it occurs. However, apart from the Makirovana Tsihomanaomby Reserve, which is the nearest protected area to the area of occupancy of V. zigzag , but which lies ca. 10–30 km inland, this zone lacks any protected areas. We judge this to be a significant shortcoming to the existing protected area network.

Paratypes. MADAGASCAR. SAVA [Antsiranana]: Ampandrozonana, ca. 2 km au Sde Sambava, 14°16′S 50°11′E, 0 m, 28 Feb. 1989, Miller 4267 (MO, P, TAN); Fkt.Manakana, à l’E du village d’Ambondrobe , 13°43′06″S 50°05′52″E, 15 July 2003, fr., Rabehevitra et al. 339 (MO, P, TAN); same loc., 13°41′57″S 50°05′19″E, 29 Oct. 2002, fr., Rabevohitra et al. 4239 (G, MO, P, TAN); same loc., 13°41′48″S 50°05′18″E, 53 m, 14 Mar. 2004, fl., Rabevohitra et al. 5163 (MO, P, TAN); Vohémar, forêtlittoraled’Ambondrobe , 13°42′46″S 50°05′25″E, 20 May 2004, Razakamalala & Rabehevitra 1351 (G, MO, P, TEF); forêt littorale au Sde Sambava, 1–10 May 1967, fl. & buds, Service Forestier 27708 (G, P, TEF).

Figures

Figure 4. Vitex zigzag Callm. & Phillipson. ––A. Branch with two inflorescences. ––B. Detail of an inflorescence with flower. ––C. Detail of fruit. ––D. Branch with infructescence. A, B based on Rabenantoandro 1402 (TAN). C, D based on Rabevohitra et al. 4239 (TAN). Drawing: Roger Lala Andriamiarisoa.