Chapelieria magna, a new species of Rubiaceae from eastern Madagascar

Abstract A new species of Chapelieria was discovered during a recent field trip to the Masoala National Park in eastern Madagascar, and is described here as Chapelieria magna Kainul., sp. nov. This species is readily distinguishable from previously described species of the genus by its quadrangular shoots, triangular-calyptrate stipules, sessile leaves, pubescent styles, and ridged fruits. It also differs in the larger number of ovules and the much larger size of leaves and fruits.


Introduction
Chapelieria A. Rich., is a genus endemic to Madagascar that belongs to tribe Octotropideae (Rubiaceae; subfamily Ixoroideae). Th e taxonomic history of the genus is complex (Madagascar Catalogue 2014). Chapelieria madagascariensis A. Rich. was originally described by Richard (1830), commemorating Louis Armand Chapelier who had collected the type material in eastern Madagascar. However, the name was fi rst published by De Candolle in September 1830, citing Richard's (1830) manuscript that was not published until December that same year (Stearn 1957). De Candolle's (1830) description is essentially identical, but with an added note on the similarity of the plant habit to that of an Apocynaceae. Baillon (1880), considered Chapelieria and Tamatavia Hook.f. as congeneric. Tamatavea melleri had been described by Hooker (1871: pl 1090) just a few years earlier although with some reservation as to its novelty: "I advance this genus as new with some hesitation, because it may prove to be one of the several Madagascarian genera which are so imperfectly or incorrectly characterized in systematic works, that it is impossible to recognize them by their description". Schumann (1891), included Tamatavia melleri in Chapelieria as C. melleri , and Chevalier (1942) subsequently synonymized the two names.
In a revision of Malagasy Apocynaceae, Pichon (1949) noted that the type material of Chapelieria madagascariensis was mixed and included both Apocynaceae and Rubiaceae material, and consequently he synonymized the name under Carissa edulis Vahl var. septentrionalis Pichon. Th e Apocynaceae specialists Markgraf (1976), and Leeuwenberg and van Dilst (2001), also considered Chapelieria a synonym of Carissa . Recently, however, Davies and Davis (2014), emended the description of Chapelieria madagascariensis and specifi ed one of the Chapelier specimens as the holotype (a paper to clarify the issue of the typifi cation is in preparation, Davis AP, pers. comm.). Th ey also described two new species of Chapelieria ( C. multifl ora N.M.J. Davies & A.P. Davis and C. septentrionalis N.M.J. Davies & A.P. Davis), and estimated the total number of species in Madagascar to be about ten.
During a recent fi eld trip to southern Masoala National Park, we collected an unknown Chapelieria and it is here described as a new species. Morphologically, the plant conforms to the characterization of tribe Octotropideae by Tosh et al. (2008), having articulated petiole bases with distinct sutures, paired supra-axillary infl orescences, hermaphroditic fl owers with secondary pollen presentation, funnelform corollas with left-contorted aestivation, 2-locular ovaries with axile placentation, pendulous ovules, and striate pattern of the seed coat. Characters that support a placement in Chapelieria as described by Davies and Davis (2014), include the sessile infl orescences, sessile fl owers, 5-merous fl owers, and seeds with entire endosperm. In contrast, the new species does not have grooved/ridged styles, and further broadens the generic description of Chapelieria (Davies and Davis 2014) by having stipules fused to a cap that cover the apical buds, sessile leaves, simple styles (not club-shaped), and in the larger number of ovules per locule (16 vs. 3-7). Furthermore, the styles of this species are sparsely pubescent, and the fruits are distinctly ribbed. Th e latter two traits are also be found in the genus Flagenium Baill. Characters that distinguish Flagenium from Chapelieria include the presence of both erect and pendulous ovules, and the absence of articulated petioles (Ruhsam and Davis 2007). Preliminary molecular phylogenetic analyses of both cpDNA and rDNA data support a position of the new species in Chapelieria (Kainulainen et al. unpublished data).
Flower buds of Chapelieria are enclosed by calyptrate bracts (Chevalier 1947), and this is also the case in Chapelieria magna . Th e conical sheath formed by the fused bracts is split by the expanding fl ower buds, but the bracts persist as an asymmetric triangular sheath around the infl orescence branches. Lateral buds appear to form continuously, and many buds of varying levels of development are found within the cymose infl orescences. However, because of the congested nature of the infl orescence, branchlets with primordial buds may appear as single bracteolate fl owers.

Distribution and habitat.
Chapelieria magna is only known from the type collection, made from a small stand of understory treelets in the rainforest of southern Masoala National Park. Notably, Chapelieria madagascariensis also occurs in this area. Although previously only known from the (eastern) Masoala peninsula by a collection made in 1951 (A. Tata 3404-RN; Davies and Davis 2014), we collected a specimen 4.7 km south of the C. magna locality in the nearby Tampolo littoral forest ( Razafi mandimbison et al. 1217A ; S, TAN). However, whereas Chapelieria madagascariensis was found on sandy soil (cf. Davies and Davis 2014), the habitat of C. magna was on lateritic soil.
Phenology. Both fl owers and fruits were found when we collected Chapelieria magna in mid-January. Th is is during the rainy season in Madagascar.