Dombeya sevathianii Le Péchon & Baider, 2011

Péchon, Timothée Le, Baider, Claudia, Gigord, Luc D. B., Haevermans, Agathe & Dubuisson, Jean-Yves, 2011, Dombeya sevathianii (Malvaceae): A new critically endangered species endemic to Mauritius (Indian Ocean), Phytotaxa 24, pp. 1-10 : 2-6

Dombeya sevathianii Le Péchon & Baider , sp. nov. ( Fig 1 & Fig. 2 )

Foliis cordatis, ovato-acuminatis, integris glaberrimis. Flores subcorymbosi, pedunculo communi et dichotomo elevati, saepuis cum flore in unaquaque, dichotomia longius pedicellato. Calyx duplex persistens, exterior bracteiformis, monophyllus. Stamina filamenta 15–20.

Type: MAURITIUS. Black River Gorges National Park, Brise-Fer road before Juniperus bermudiana (Cyprès) plantation leading to ‘Camp field station’, near the roadside, facing the Mare Longue Reservoir, degraded forest invaded by Psidium cattleianum , 20°23’01.8”S, 57°27’04.9”, 595 m, 12 May 2004, (fl), J. C. Sevathian s.n. ( MAU 23856; holotype MAU).

Tree 3–8 m tall, dbh 3–10 cm, deciduous, probably hermaphroditic. Bark dark gray, smooth. Ultimate branches light green, with numerous contrasting whitish scars (from leaves and stipules), glabrous. Leaves alternate, glabrous; lamina 4.0–9.5 × 2.6–7.0 cm, ovate, base cordate, apex acute, margin entire, glabrous; venation palmate with 5 primary veins; petiole whitish green, glabrous; stipule present, 3.0–5.5 × 0.5–1.0 mm, subulate, fugacious, glabrous. Inflorescence pedunculate, axillary, peduncle 20–31 mm long, glabrescent with few stellate hairs. Inflorescence organized in biparous pseudo-cyme, the distal ramifications being irregular giving a branching coral-like aspect, each ramification presenting two linear small bracts. Pedicels glabrous.

Epicalyx cupuliform, formed by one bract, 2.3–4.1 × 1.35–2.40 mm, persistent, glabrous. Flower, sepals valvate, persistent (4–)5, 2.4–4.0 × 1.0– 1.7 mm, triangular acute, shortly fused at the base, abaxial surface light-green, adaxial surface light-green with pinkish base, glabrous, opened but not reflexed along the pedicel; petals 5, persistent, convolute, 2.15–3.25 × 3.4–5.1 mm, white, almost symmetric; staminal tube caducous, 0.95–1.85 mm, same colour as petals; stamens, 15–20, 1.30–2.45 mm long, free part of filaments 0.4–1.5 mm long, anther 0.85–1.00 mm. Ovary rounded, 0.55–1.00 × 0.8–1.4 mm, pubescent with few stellate and glandular trichomes; style caducous, absent or very short, 0.10–0.35 mm; stigmatic branches 5, 1.3–3.5 mm. Ovules two per locule, placentation axile. Capsule (4–)5-locular, 0.40 × 0.55 cm, globose, sparsely pubescent with a few stellate hairs, tardily dehiscent. Seeds triangular elliptic, longitudinally compressed on one side, brown with dark brown marbled veins, surface tuberculated, (2.8–)3.1(–3.6) × (1.6–)2.0(–2.3) × (1.45–)1.80(–2.05) mm.

Distribution and habitat:— MAURITIUS. Endemic. The species is known to grow between latitudes 20 0 22’07’’–20 0 23’01’’ S and longuitudes 57 0 26’25’’–57 0 27’04’’E, at 550–600 m elevation ( Fig. 3 ), on plateau developed by ‘early lavas’ (3.5–2 Mya) on ferralitic soil (Willaime 1984). The area receives 2,300 –2,600 mm of rainfall annually (Willaime 1984), with mean annual temperatures of about 20 0 C ( Halais & Davy 1969). The species occurs in the upland forest sensu Vaughan & Wiehe (1937), with canopy not exceeding 7 m in height and emergents up to 10 m tall, but most plants are found in a more shrubby vegetation of 3–6 m tall. The species grow with the emergent Sapotaceae Sideroxylon cinereum Lam. , Sideroxylon puberulum DC. , Labourdonnaisia glauca Bojer , Labourdonnaisia calophylloides Bojer and Labourdannaisia revoluta Bojer , and with the canopy/understory Warneckea trinervis (DC.) Jacq. -Fél. ( Melastomataceae ), Securinega durissima J.F.Gmel. (Phyllanthaceae) , Diospyros tessellaria Poir. (Ebenaceae) , Molinaea alternifolia Willd. (Sapindaceae) , Erythrospermum monticolum Thouars (Achariaceae) , Eugenia kanakana N.Snow and Syzygium glomeratum DC. (both Myrtaceae ), Ixora parviflora Lam. (Rubiaceae) , Acalypha integrifolia Willd. (Euphorbiaceae) , with the liana Cnestis glabra Lam. (Connaraceae) and the herbaceous Carex brunnea Thunb. (Cyperaceae) . These native forests are invaded mainly by Psidium cattleianum Sabine (Myrtaceae) and Ligustrum robustum Thwaites subsp. walkeri (Decne.) P.S.Green (Oleaceae) , and the shrubs Wikstroemia indica ( L.) C. A.Mey. ( Thymelaeaceae ), Ossaea marginata and Clidemia hirta (both Melastomataceae ).

Surprisingly it grows sympatrically with another rare Dombeya : D. mauritiana Friedmann (1981: 439) , a species thought to be extinct in the wild, but was recently rediscovered but is known only from a single wild adult ( Florens 2009).

Conservation:— Dombeya sevathianii was known from a single adult plant until 2009, when eight other individuals were found. Of these nine plants only three are adults. The isolated plant found in 2004 grows about 2 km from a clump of one adult and 5 saplings (between 0.5–2.0 m high). In between, the third adult (and one sapling) is found at about 0.2 km from the clump. No other plants have been found despite the intensive search in the region (200 person hours). Besides, in 2011, we noticed that the first plant found in 2004 (the type specimen) is now dying, further reducing the effective population size. Consequently, due to its extreme small effective population, restricted area of occupancy (<25 m 2) and area of occurrence (<0.06 km 2, calculated using Google Earth and GE Path v 1.4.4a as per the Sampled Red List Index for Plants 2010), Dombeya sevathianii is hereby considered as Critically Endangered ( CR B 1, B 2a, b(iii), D) according to the IUCN Red List Criteria ( IUCN 2001).

All known plants occur inside a protected area (the Black River Gorges National Park) in forest areas that have not been logged or subjected to any form of agricultural or pastoral use and that are situated far from other human developments. However, the areas are highly invaded, typically by alien tree species, whos stems sum up to about 75% all woody plants with DBH> 1cm ( Florens 2008), although they are considered in Mauritius to be of high to medium quality (with> 50% native canopy cover). A species recovery plan and active conservation management is urgent for ensuring the long-term survival of this and several other rare endemic species.

All three adults produce viable seeds, that germinate from 1½ months to up 1½ years. However, successful germination rates are small (20–36%) (Baider & Florens, unpubl. data). Such low rates of germination could be related to low pollination rates because of lack of pollinators (introduced bees were observed to visit the flowers) or low rate of cross pollination (adults are far apart), but also insect damage on the developing fruits was commonly observed.

Six seedlings were found at the base of the isolated tree in 2007 but they were not alive a year later, but saplings are growing near the other clumps where vegetation is shorter and more open. It is known that native species growing in forests heavily invaded by alien plants show substantial reduction in fitness including reproductive output ( Baider & Florens 2006). Furthermore, it has been shown that native butterfly species richness and population densities are much lower in such invaded areas ( Florens et al. 2010), suggesting a paucity of pollinators in alien invaded forests, since butterflies are often used as an indicator group for other insects. However, control of invasive alien plants can revert these trends ( Florens 2008). Therefore, control of alien weeds should be a priority for the in-situ conservation of the species. This can be supplemented with propagation by seeds ex-situ in a local nursery in view of re-enforcing the existing population. The species should also be maintained in ex-situ facilities to support in-situ conservation, but care must be taken that it does not hybridize with other Dombeya species. Further surveys are recommended since the species may potentially grow in a wider area of remaining good quality native forest than currently known.

Etymology:—The epithet refers to botanist Jean-Claude Sevathian, the first collector of this new species and Plant Conservation Officer at local NGO Mauritian Wildlife Foundation and Forest Conservation Consultant.

Phenology:— Dombeya sevathianii flowers from April to June; flower buds in November ( C. Baider 2010, pers. obs.). Fruiting from July to August (Le Péchon 143 & Sevathian; Le Péchon 1026 & Sevathian; Le Péchon 1028 & Sevathian), extending up to November ( C. Baider 2010, pers. obs.).

Additional material examined:— MAURITIUS. Black River Gorges National Park , 20°22'9.57"S, 57°26'31.43"E, 596 m, 14 June 2010 (fr), Le Péchon 1026 & Sevathian ( MAU, REU) ; Black River Gorges National Park 20°22'6.41"S, 57°26'25.44"E, 559 m, 14 May 2010 (fr), Le Péchon 1028 & Sevathian ( MAU, REU) ; Black River Gorges National Park, Brise Fer , 20°23’01.8”S, 57°27’04.9”, 595 m, 4 July 2010 (fr), Le Péchon 143 & Sevathian ( P); Black River Gorges National Park, road to Brise Fer, 20°23’01.8”S, 57°27’04.9”, 595 m, 13 May 2004 (fl), Sevathian s.n. MAU 23855 ( P) .; Black River Gorges National Park , 20° 22’ 09.7’’S; 57° 26’ 31.1’’ E, 602 m, 3 May 2009 (fl.), V . Florens & Baider 2116 ( MAU 24933) .

Figures

FIGURE 1: Dombeya sevathianii. A. Habit. B. Inflorescence. C. Lower surface of the leaf. D. Inflorescence architecture and flowers. E. Fruit F. and G. The two distinct morphologies of flowers (E, F and G are drawn to the same scale).

FIGURE 2: Morphological characters of Dombeya sevathianii A. Habit. B. and C. Branchlet showing inflorescences. D. Bark. E. Upper surface of the leaf. F. Lower surface of the leaf. G. Stipule and leaves scars. H. Inflorescence architecture. I. Inflorescence bracts. J. Floral buds and epicalyx. K. Inflorescence. L. and M. Flowers (note lack of staminodes). N. Immature fruit. O. Seedling (Photographs A, D, L, M & N by Jean-Claude Sevathian, B, C, K, O: by F. B. Vincent Florens).

FIGURE 3. Distribution map of Dombeya sevathianii in Mauritius.