Gravesia serratifolia Almeda & H. Ranariv., 2019

Almeda, Frank & Ranarivelo, Heritiana, 2019, Gravesia serratifolia (Melastomataceae: Sonerileae), a new species from Marojejy National Park, Madagascar, Phytotaxa 391 (2), pp. 115-121 : 116-120

Gravesia serratifolia Almeda & H. Ranariv. , sp. nov. ( Figures 1 & 2 )

Diagnosis: Distinguished from all Gravesia species by a combination of small (1−3.3 × 0.7−2.7 cm) coarsely serrate leaf blades that are moderately lepidote on both surfaces like young vegetative buds, calyx tube well-developed and flangelike, 1.5 mm long; calyx lobes obsolete or evident as depressed truncate undulations, calyx teeth 5, 0.75−1 × 0.5−0.75 mm, prominent and prolonged beyond calyx tube, laterally compressed when fresh but appearing knobby and callose-thickened when dry; filaments sparsely to moderately beset with rufescent simple (rarely branched) glandlike trichomes mostly less than 0.25 mm long that are commonly clustered or fascicled, and anther connective conspicuously prolonged dorso-basally ca. 0.5 mm above the junction with the filament into a linear-oblong widely spreading or coiled appendage 0.5−0.75 mm long.

Type:— MADAGASCAR. Antsiranana: SAVA, Andapa, Marojejy National Park , top of the massif, 2132 m, 14°26’57”S, 49°43’57”E, 13 December 2005, fl., H. Ranarivelo & D. Ravelonarivo RHS 857 (holotype: CAS!; isotypes: G!, MO!, P!, TAN!) .

Sparingly branched shrub 50 cm to 1 m tall. Distal cauline internodes rounded-quadrate, deeply and inconspicuously canaliculate on two of the opposing faces, essentially glabrous, sparingly and irregularly lenticellate. Cauline nodes somewhat swollen at the base of each petiole with elevated somewhat pustulate U-shaped or V-shaped interpetiolar lines. Leaves opposite and decussate, isomorphic in size and shape in each pair, ± erect or ascending when fresh, the adaxial surface sometimes ± convex or with the blade margins curved downward at a gentle angle when fresh. Leaves semi-succulent when fresh becoming chartaceous when dry; petioles 3.5−6 mm long, canaliculate and glabrous on the adaxial surface, rounded and glabrous to lenticellate on the abaxial surface; blades bright green when fresh, irregularly flushed red along the margins, 1−3.3 × 0.7−2.7 cm, elliptic-ovate to ovate or suborbicular (rarely ovateobovate), 5-nerved with inconspicuous acarodomatia where the inner pair of secondary veins diverge from the primary vein at the blade base, moderately and randomly lepidote on both surfaces like the young vegetative buds, the scales minute, sessile, and rusty brown, apex obtuse to rounded, base obtuse to bluntly acute or nearly rounded, the blade margins conspicuously and coarsely serrate for much of their length. Inflorescence a terminal simple dichasium of three flowers but often reduced to a solitary flower or occasionally somewhat congested and 5-flowered on an erect solitary peduncle (4−) 7−16 mm long; pedicels 2−4 mm long, glabrous, lenticellate and sometimes also sparingly rusty lepidote, the subtending bracts with petioles mostly 1 mm long and blades 2−5 × 1.5−4 mm, elliptic-ovate to obovate, 3-nerved, apex obtuse, base acute to cuneate, sparingly rusty-lepidote on both surfaces, the margins coarsely serrate; the bracteoles 1.5−2.5 × 0.25−0.5 mm, linear-oblong to narrowly oblanceolate, obscurely 1-nerved, apex narrowly acute, base narrowly attenuate, glabrous, the margins entire. Hypanthium (at anthesis) 4−5 mm long to the torus and 4−5 mm in diameter, broadly turbinate to infundibuliform, ± terete or only 2-costate on some hypanthia, essentially glabrous, often irregularly lenticellate and sparingly beset with a sessile rusty-lepidote indumentum that is caducous; calyx tube well developed and flangelike, 1.5 mm long; calyx lobes obsolete or evident as depressed truncate undulations, calyx teeth 5, 0.75−1 × 0.5−0.75 mm, prominent and prolonged beyond calyx tube, laterally compressed when fresh but appearing knobby and ± callose-thickened when dry. Petals 5, 13−19 × 6−9 mm, narrowly obovate, obliquely apiculate at the apex, magenta, entire and eciliate. Stamens 10, isomorphic in size and shape, erect and ± clustered around the erect style at anthesis; filaments 6−7 mm long and 0.5 mm in diameter, pale pink, compressed, sparsely to moderately beset with rusty brown simple (rarely branched) glandlike trichomes mostly less than 0.25 mm long that are commonly clustered or fascicled; anther thecae 4 mm long and 1 mm in diameter, yellow, oblong, ± laterally compressed, the apical pore ventrally inclined; connective conspicuously thickened dorsally and prolonged dorso-basally ca. 0.5 mm above the junction with the filament into a linear-oblong widely spreading or coiled appendage 0.5−0.75 mm long. Ovary (at anthesis) 3 mm long and 2 mm in diameter, bluntly oblong-elliptic and somewhat tapered distally (at anthesis), glabrous, apex truncate to rounded, 1/3-inferior, 5-locular; style 10−12 mm long and 0.5−0.75 mm in diameter, pale pink but whitish distally, terete and ± straight, glabrous and terminating in a punctiform stigma. Mature capsules and seeds not seen.

Phenology:—The type and two of the paratypes, which were collected in October and December, are in flower; these flowering specimens have a few post-mature ruptured capsules with no seeds. One other paratype that was collected in November has young fruits. Another paratype collected outside of Marojejy NP in March is in post-mature fruit.

Habitat and distribution:—Three of the five known collections of Gravesia serratifolia were collected at or near the summit of Marojejy National Park above 2000 m elevation ( Figure 3 ). The fourth collection was purportedly made near Camp III. Our GPS readings in the field indicate that Camp III is at about 1319 m. We did not see this species around Camp III so we suspect that this collection was made at a somewhat higher elevation in ericoid vegetation. The single collection from outside the park boundaries was made at 1774 m. Four natural vegetational formations have been identified on the Marojejy Massif ( Humbert 1955; Garreau & Manantsara 2003): humid dense forests occur below 800 m; medium-elevation rainforests occur between 800 and 1400 m; dense montane forests are found between 1400 and 1800 m; and what has been described as ericoid vegetation ( Humbert 1955) or montane thicket ( Garreau & Manantsara 2003) occurs above 1800 m. Most of the known collections of G. serratifolia were made in this latter formation which covers only about 1000 ha or 1.5 % of the area of Marojejy National Park.

Conservation status:— Gravesia serratifolia is mostly known from a limited area at upper elevations of Marojejy National Park and one outlying montane site northwest of the park. The EOO is 36.9 km ² and the AOO is 8 km ². Except for the single collection made outside of the park, all known populations of this species occur within the boundary of Marojejy National Park. Populations in the park are afforded some protection so it seems unlikely that they are severely threatened at this time. The lower elevation forests within and surrounding Marojejy NP suffer from diffuse but regular noncommercial pressure due to exploitation of forest products. Ecotourism at Marojejy NP is small-scale at present but increased human visitation to the high elevation montane thicket vegetation could become a potential threat because of its limited extent and the slow growth of plant species in this fragile formation ( Garreau & Manantsara 2003). To date there has been no history of fire damage to the vegetational cover in the interior of Marojejy NP ( Garreau & Manantsara 2003). However, low elevation habitats outside of the national park continue to experience out-of-control fires and areas in the Betaolana corridor are threatened by mining sites for topaz and beryl. In view of its limited area of occupancy, small population size (surely less than 1000 individuals), and number of known locations (≤ 5), we recommend a conservation classification of Vulnerable (VU): D2 for G. serratifolia at this time.

Etymology:—The epithet for this species, serratifolia , highlights the conspicuous serrate foliar margins that extend for most of the length of each mature leaf blade.

Additional specimens examined:— MADAGASCAR. Antsiranana: Massif de Marojejy , sommet face ouest, 2000–2137 m, [14°26’55.41”S, 49°43’59.89”E], Nov. 1972, yg. fr., Morat 4091 ( P, TAN!) ; Marojejy-Andapa, forêt à mousse Camp III, [14°26’11.7”S, 49°44’36.9”E], 11 Oct. 1988, fl., Rakatozafy & Raharilala 2258 ( TAN!) ; SAVA, Andapa, Marojejy National Park , top of the massif, 2132 m, 14°26’57”S, 49°43’57”E, 13 Dec. 2005, fl., Ranarivelo & Ravelonarivo RHS 820 ( CAS!, MO!, TAN!) ; Anjialavabe et Doany, Andapa , deuxième montagne d’Ankarongameloka , 1774 m, 14°14’S, 49°26’E, 11 Mar. 2006, old fr., Ravelonarivo et al. 1872 ( MO, P-online image!, TAN) .

Discussion:— Perrier de la Bâthie (1932, 1951) divided Gravesia into three subgenera. The subgenus Gravesia , to which he assigned over 100 described species, was further divided into four sections largely based on habit and inflorescence architecture. The taxonomy of Gravesia in Madagascar has received little attention since Perrier de la Bâthie’s flora treatment of the genus. The monophyly of its infrageneric groupings are yet to be tested in a phylogenetic context. Several of the sections in subgenus Gravesia include morphologically diverse species. We tentatively assign G. serratifolia to section Pauciflorae based on its shrubby habit with stems that exceed the leaves in length and few-flowered cymose inflorescence, but it does not match or appear to be particularly close to any of the species assigned to this section by Perrier de la Bâthie (1951).

Gravesia serratifolia is readily distinguished from its congeners by the combination of coarsely serrate leaves that are elliptic-ovate to ovate or suborbicular, basally nerved and randomly beset with a minute lepidote indumentum on both surfaces ( Figures 1B–E ), flangelike unlobed calyx with prominent calyx teeth ( Figures 1J, K ), and rufescent trichomes on the filaments that are mostly clustered or fascicled ( Figures 1G–I ). Its closest relative appears to be G. rubra (Jum. & H. Perrier 1911: 274) H. Perrier (1932: 132) , a species that Perrier de la Bâthie (1951) assigned to section Macrophyllae because of its large shrubby habit and paniculate inflorescence with an elongate peduncle and well-developed branches. Both G. rubra and G. serratifolia are similar in having glabrous rounded-quadrate distal internodes, 5-nerved leaves, glabrous hypanthia, conspicuous calyx teeth, and filaments that are beset with trichomes. Gravesia rubra differs most notably in being completely glabrous and in having much larger (5−8 × 1.3−2.2 cm) narrowly elliptic to elliptic-lanceolate leaves that are dentate and attenuate both apically and basally. It also differs from G. serratifolia in having broadly deltoid calyx lobes and filaments that are inconspicuously glandular pilose with the translucent solitary glands mostly less than 0.125 mm long (vs. simple or rarely branched rufescent trichomes mostly less than 0.25 mm long that are commonly clustered or fascicled). We initially considered the possibility that G. serratifolia might be a close relative of the sympatric G. marojejyensis Humbert (1955: 118) which is also endemic to high elevations on the Marojejy massif and known only from the type collection. When Humbert described the latter he assigned it to Gravesia sect. Primuloideae based on its repent radicant suffrutescent habit with elongate internodes, few-flowered contracted umbelliform cymes, and inflorescence peduncles that are longer than the pedicels. Both G. serratifolia and G. marojejyensis share similar broadly turbinate to infundibuliform hypanthia and few-flowered inflorescences. The latter, however, does not appear to be closely related based on its broadly elliptic to nearly orbicular leaves that are coarsely denticulate, cordate at the base, conspicuously bullate on the adaxial surface, and beset with conspicuous rufescent trichomes on the elevated abaxial leaf veins and distal internodes. It also differs markedly from G. serratifolia in having a sparse cover of smooth spreading hypanthial trichomes, well-defined broadly deltoid calyx lobes, white petals with a yellowish flush on the abaxial surface, glabrous filaments, and blunt obtuse dorso-basal deflexed staminal appendages. In leaf shape and size and the few-flowered cymose inflorescences, G. serpens H. Perrier (1945: 101) and G. venusta H. Perrier (1932: 107) are somewhat reminiscent of G. serratifolia but both of these species belong to sect. Scandentes which consists of species that are consistently climbing epiphytes with clinging roots. The leaves of both of these species also differ in having consistently cordiform bases (vs. obtuse to bluntly acute or nearly rounded) and the margins are uniformly entire (vs. coarsely serrate).

Figures

FIGURE 1. Gravesia serratifolia. A. Habit. B. Representative leaf (abaxial surface) C. Representative leaf (adaxial surface). D. Enlargement of a portion of abaxial leaf surface showing serrate margin and scattered lepidote indumentum. E. Enlargement of abaxial leaf base showing acarodomatia where secondary veins diverge from primary vein. F. Petal (adaxial surface) G. Stamen (profile view). H. Enlargement of filament showing fascicled glandlike trichomes. I. Enlargement of filament showing solitary and branched glandlike trichomes. J. Hypanthium and style (at anthesis) with petals and stamens removed. K. Simple dichasium showing bracts and bracteoles. Drawn from Ranarivelo & Ravelonarivo RHS 857.

FIGURE 2. Gravesia serratifolia showing habit, leaves, inflorescence, and flower. (Photo: Éric Mathieu)

FIGURE 3. Geographic distribution of Gravesia serratifolia.