Schizolaena isaloensis, Rabehevitra & Lowry, 2009

Rabehevitra, David & Lowry Ii, Porter P., 2009, Endemic Families of Madagascar. XI. A new critically endangered species of Schizolaena (Sarcolaenaceae) from Tapia woodland in south-central Madagascar, Adansonia (3) 31 (1), pp. 149-155 : 151-154

Genus Schizolaena Thouars

Schizolaena isaloensis

Rabehevitra & Lowry, sp. nov. ( Figs 1 ; 2 )

Haec species a Schizolaena microphylla foliis ambitu plus variabilibus (ellipticis usque ovatis obovatisve), apice acutis usque subrotundatis (interdum emarginatis), venatione secundaria prominente, costa abaxialiter indumento vestita atque petalis minoribus spatulatis basem versus angustatis differt.

TYPUS. — Madagascar. Prov. Fianarantsoa, Fivondronana Ranohira, PK 742 on Route Nationale 7, c. 20 km WSW of Ranohira, [anthropogenic grassland near remnant] sclerophyllous evergreen forest [woodland], 22°46’32”S, 45°00’47”E, 1023 m, 14.IX.2005, fl., y.fr., Randrianarivelo, Rabehevitra, Rakotoarivony, Randriatsivery & Rasoafaranaivo 254 (holo-, MO!; iso-, G!, K!, P!, TEF!, WAG!).

PARATYPES. — Madagascar. Prov. Fianarantsoa, plateaux et vallées de l’Isalo à l’W de Ranohira, grès et sables siliceux, [22°28’S, 45°20’E], 800-1250 m, 29.I-2.II and 8-10.IV.1955, ster., Humbert 29766’A’ ( P). — 2 e col des Tapias, à la sortie d’Isalo, [22°47’S, 45°00’E], VII.1969, ster., Morat 3367 ( TAN). — Isalo, bois de Tapia, grès, 900 m, X.1924, fl., Perrier de la Bâthie 16589 ( K, MO, P). — Isalo, degraded woodland 4 km E of Ilakaka River , 22°40’44”S, 45°15’21”E, 840m, 19.III.2005, ster., P . B . Phillipson et al. 5804 ( MO, P, TEF). — Ranohira, PK 712, [22°38’S, 45°20’E], 23.VII.1951, ster., Service Forestier 13891 ( P). — Massif gréseux de l’Isalo, à l’ouest de Ranohira, [22°28’S, 45°20’E], 17-18. VI .1958, ster., Service Forestier (Capuron) 18567bis ( P). — Isalo, Ilakaka, plaine, sol sabloneux, [22°41’S, 45°13’E], 23.VII.1955, ster., Service Forestier 218-R-239 ( P). — Tapia de l’Isalo , Canton de Ranohira , 21.VII.1954, ster., Service Forestier 137-R-141 ( P) .

DESCRIPTION

Trees c. 4-10 m tall, bark thick, spongy.Twigs with stellate indumentum. Leaves elliptic to ovate or obovate, dark green and shiny above (paler in dry material), pale green below, subcoriaceous, 1.4- 3.3(-4) × 1.2-2.1(-2.6) cm, with minute stellate indumentum on abaxial surface primarily along the midvein and secondary veins, nearly glabrous or sparsely stellate on adaxial surface (densely stellate in young leaves), especially on the midvein, apex acute to nearly rounded, sometimes retuse, margin entire, minutely thickened, slightly revolute, base broadly rounded or slightly subcordate to cordate, venation brochidodromous, with 4 or 5 pairs of alternate to subopposite, prominent secondary veins joined by rounded arches, distinctly raised on abaxial surface, midrib weakly channeled above, raised below; petiole 2-4 mm long, with dense stellate indumentum; stipules lanceolate to broadly triangular, pale yellow green, membranous, with nearly obscure parallel venation, 3-4 × 1-1.5 mm, apex acute, base truncate, caducous, leaving a small scar. Inflorescence comprising 1 or 2 (rarely 3) unbranched axes, each with a pair of bracts borne near the middle and bearing 1 or 2 terminal flowers, or rarely a small raceme with 2 or 3 alternate branches, subtended by a pair of bracts, each bearing 1 or 2 flowers, axis 3-4(-6) mm long, densely papillose stellate-strigose, bracts broadly triangular to cordate or nearly circular, 2 × 1.5-2 mm, apex rounded to acute, papillose on both surfaces, with stellate indumentum along the margins, rarely caducous, ultimate axes below the involucre 1.5-2 mm long, densely papillose stellate, involucre in flower with 5 irregular lobes, densely papillose on both surfaces, with stellate indumentum along the margins of the teeth, containing 1 or 2 sessile flowers; sepals 3, imbricate, broadly ovate, adaxially concave, 4-5 × 4 mm at anthesis, glabrous on adaxial surface, with short stellate-papillose indumentum on abaxial surface, apex rounded to acute, margins entire; petals 5, spatulate, narrowed at base, slightly succulent in fresh material, chartaceous when dry, 5-6 × 3 mm, stellate on abaxial surface (sparsely stellate to glabrous toward margins), glabrous on adaxial surface, with minute white striations (in dry material), apex rounded to broadly acute; stamens c. 20, filaments slender, c. 3 mm long, glabrous, anthers elliptic to nearly circular, 0.3-0.4 mm long, introrse, dehiscent through apical to longitudinal slits; ovary broadly depressed ovoid in fresh material, to depressed globose in dry material, c. 1 mm in diam., densely white woolly tomentose, 3-locular; style cylindrical, very slightly curved at anthesis, c. 1.5 mm long, stigma terminal, circular, glabrous. Young fruit subglobose, 5-7 mm in diam., with dense papillose stellate indumentum, exocarp cartilaginous, rugose, dry sepals and filaments persistent; involucre expanded, broadly funnelform to somewhat cupuliform, hiding the fruit, light green in fresh material, abaxial and adaxial surfaces sparsely glandular papillose, with 5 broadly ovate to narrowly elliptic, unequal lobes divided ⅓ to ½ of the

45°E 50°

15°S

20°

25°

way to the base, each lobe with 9-12(-14) narrowly cylindrical to filiform processes 2.5-4(-5) mm long; seeds 1 or 2 per locule, broadly spherical to ovoid, yellow, 3-4 mm long, 3-5 mm in diam., hylum depressed concave; mature fruit unknown.

REMARKS

A total of seven mature individuals of Schizolaena isaloensis were recorded at the site where the type material was collected, situated in open, highly degraded grassland ( Fig. 2A ) c. 4 km from the nearest remnant stand of Tapia woodland. Fewer than 30 adult plants of various sizes were observed at the only other recently recorded site c. 30 km to the NE where Phillipson et al. 5804 was collected. A careful survey of the type locality failed to reveal any seedlings or juvenile individuals. Moreover, observations made over the last several years by botanists passing through the area indicate that it is subjected to regular annual burning, and while adult trees, with their thick and spongy bark, are clearly adapted to withstand fire, seedlings and young individuals apparently can not survive repeated burning, although some re-growth was observed at both sites, including from two trees that had been cut at the type locality.

The only fertile material of Schizolaena isaloensis (the type gathering) was collected late in Madagascar’s dry season when very few species flower in this part of the country. Botanists passing through at this time of year typically do not stop to conduct field work, which may explain why no fertile collections of our new species had previously been gathered even though several large, isolated trees are easily visible from the main road.

Using the key to species of Schizolaena provided by Lowry et al. (1999), material of this new species would be identified as S. microphylla based on the small size of its leaves. These two taxa can, however, be distinguished from one another by several foliar and floral features, combined with their different substrate preferences and geographic distributions ( Fig. 3 ), as summarized in the Table 1.

The Isalo area represents the southern limit of Tapia woodland, and it is possible that populations of Schizolaena once occurred at sites located between the known ranges of S. isaloensis and S. microphylla . If such populations existed, they may have comprised individuals that exhibited morphologies intermediate between these two species. However, since no plants have been recorded from anywhere within the c. 225 km distance separating S. isaloensis and S. microphylla , and in view of the unambiguous morphological differences that distinguish them, we consider it best to treat our new taxon as distinct at the species level.

CONSERVATION STATUS

Schizolaena isaloensis is currently known only from a very restricted area of highly disturbed anthropogenic grassland outside the southern limit of Isalo National Park, along Route Nationale 7, although a few collections made more than 50 years ago appear to have come from other nearby localities, including from within the park ( Fig. 3 ). Fewer than 10 mature individuals occur at the locality where the type material was gathered, and another c. 25- 30 trees were observed at the only other recently documented site. The absence of any seedlings or young individuals strongly suggests that no regeneration is occurring. The bark of mature trees showed clear signs of intense burning, reflecting the high level of disturbance in the area. Based on application of the IUCN (2001) threat criteria, we assign S. isaloensis a preliminary status of Critically Endangered (D) as the estimated population size is less than 50 individuals.

Figures

FIG. 1. — Schizolaena isaloensis Rabehevitra & Lowry,sp. nov.:A, fruiting branch;B, abaxial surface of leaf; C, flower;D, anther; E, im- mature fruit with developing involucre. Randrianarivelo et al. 254. Scale bars: A, B, 1 cm; C, 6 mm; D, 1 mm; E, 5 mm.

FIG. 2. — Photographs of Schizolaena isaloensis Rabehevitra & Lowry, sp. nov.: A, habitat; B, habit; C, inflorescence; D, flower; E, involucre surrounding young fruit (photos: D. Rabehevitra).

FIG. 3. — Distribution of Schizolaena isaloensis Rabehevitra & Lowry (○) and S. microphylla (▲), mapped on the bioclimatic zones of Madagascar (after Cornet 1974; see Schatz 2000).