Clerodendrum giganteum (Moldenke) Phillipson & Callm., 2016

Phillipson, Peter B. & Callmander, Martin W., 2016, Two varieties of Clerodendrum L. (Lamiaceae) from Madagascar raised to specific rank, Candollea 71 (2), pp. 373-377 : 376

Clerodendrum giganteum (Moldenke) Phillipson & Callm. , comb. et stat. nov.

÷ Clerodendrum aucubifolium var. giganteum Moldenke in Bull. Torrey Bot. Club 77: 393. 1950.

Typus: MADAGASCAR. Prov. Antsiranana: Sambirano , Massif de Manongarivo, [14°04’S 48°16’E], 200 m, V.1909, Perrier de la Bâthie 10229 (holo-: P [ P00440396 ]!; iso-: P [ P00440397 , P00440398 ]!).

Vernacular name. – “Ambora” (Antilahimena 2089).

Distribution, ecology and conservation status. – Clerodendrum giganteum is known from five localities scattered across the northern part of Madagascar, spanning the humid and subhumid bioclimatic zones, and all within Madagascar’s protected area network (Ampasindava-Galoka-Kalobinono, Makira, Manongarivo, and Marojejy). The species would appear to be relatively rare, having been collected few times despite having highly conspicuous flowers and generally occurring in areas where inventory work has been conducted. The collections have all been made in forest or woodland, frequently near streams, on a variety of substrates, at low elevations (near sea-level to 200 m) in the west and mid to high elevations (900 to 1200 m) in the east. The localities are taken to represent five separate subpopulations, none of which are known to be threatened, and no decline in the extent of occurrence or area of occupancy of the species can be projected. Clerodendrum giganteum is therefore assessed as “Least Concern” [LC] following IUCN Red List Categories and Criteria ( IUCN, 2012).

Observations. – Clerodendrum giganteum was distinguished by Moldenke (1950: 393) from typical C. aucubifolium by its much larger calyx - “ 4.5-5 cm long, flaring to 2.5 cm wide at the apex” at anthesis, and by its slender corolla tube - “up to 18 cm long”, expanding to a funnelshaped mouth, with its lobes c. 2 cm long, and a deeply lobed fruiting-calyx. The species is not known to have been collected again at the type locality (the Manongarivo Massif in north-western Madagascar), but the type can be matched with material from a number of other sites in the north of the island. The exceptionally large size of the calyx and corolla of this plant is confirmed by our study, but the stated diameter of the calyx apex was mis-reported, all of the flowers on the type collection have a calyx diameter of no more than c. 10 mm. The mouth of the corolla is considerably larger in diameter, and it is possibly this dimension that was given in error. Careful examination of the holotype and two isotypes at P, reveal considerable variation in the length of the corolla tube, and some of the open flowers of these specimens are only c. 8 cm long. This trend is seen in other specimens of C. giganteum , and we hypothesise that the corolla tube, the filaments and style might continue to expand during anthesis. Perhaps an adaptation of this kind could facilitate pollination by a range of different pollinators, but clearly field observations are needed to confirm or refute this hypothesis. Otherwise, calyx and corolla dimensions vary little among the other specimens now available. Clerodendrum giganteum can be distinguished f rom C. thouarsii by its smaller (13-18 X 4.5-5.5 vs. 13- 27 X 8-13 cm) leaves which are narrowly elliptic-obovate and membranous vs. broadly elliptic-obovate and sub-coriaceous, and also by its less contracted inflorescences with much smaller bracts (the bract subtending the inflorescence unit 3 X 3 mm vs. 13-16 X 8-10 mm, and the bract subtending the flower 7 X 1 mm vs. 15 X 2 mm). The corollas of C. giganteum generally have longer tubes, but shorter lob es than those of C. thouarsii . See Table 1 for more details of the different between the two species.

Other specimens examined. – MADAGASCAR. Prov. Antsiranana: partie occidentale du Massif de Marojejy (NE) de la vallée de l’Ambatoharanana au bassin supérieur de l’Antsahaberoka , 1000-1200 m, 9.XI-2.XII.1959, Humbert & Saboureau 31407 ( P); Bemanevika, affluent de la riv., péninsule d’Ampasindava , 13°46’03”S 47°58’52”E, 34 m, 30.I.2009, Rakotovao 4339 ( G, MO, P, TAN). Prov. Toamasina: Masoala NP , Ambohitsitondroina Mahalevona , 15°26’07”S 49°57’27”E, 1172 m, 4.X.2003, Antilahimena 2089 ( MO, P, TAN); Sahatany, Andongona , Makira , Bevory River , 15°27’55”S 49°20’10”E, 24.XI.2003, Antilahimena 2375 ( MO, P, TAN).