Labramia ambondrombeensis (Sapotaceae), a Critically Endangered new species from Madagascar.

Abstract Randriarisoa, A., Y. Naciri & L. Gautier (2020). Labramia ambondrombeensis (Sapotaceae), a Critically Endangered new species from Madagascar. Candollea 75: 83–87. In English, English and French abstracts. Timber of the family Sapotaceae are appreciated for their physical properties internationally as well as locally, which often put a serious pressure on species survival. Taxonomic efforts are badly needed before producing reliable conservation assessments for the Malagasy species. In the framework of the revision of three related Sapotaceae genera, all endemic from Madagascar and surrounding islands of the Western Indian Ocean, a new species of Labramia A. DC. has been identified. It is described and illustrated here. Labramia ambondrombeensis L. Gaut. & Randriarisoa is one of the two Labramia species that have relatively small leaves. It is compared to Labramia platanoides Capuron ex Aubrév., the other small-leaved species from which it differs in leaf shape, pedicel size and ovary cell number. Labramia ambondrombeensis is known from a single collection that comes from a littoral forest in the Northeastern coast of the island, lacking any legal protection and is preliminary assessed as “Critically Endangered” using the IUCN Red List Criteria.


Introduction
Sapotaceae is a well-defined tropical plant family of about 1250 species (Pennington, 1991;Govaerts et al., 2001). Its members are mostly large trees that are highly valued for their mechanical properties and widely used in construction. Following the rosewood crisis (Hassold et al., 2016), they are, along with Ebenaceae, the next group likely to be severely affected by illegal logging in protected areas. Almost all species are characterized by a slow growth and long generation times and can be considered, from a conservation point of view, as markers of primary forests. However, classification based on morphological data is highly controversial in this family, and generic delimitations have always been a matter of debate (e.g. Lam, 1939;Aubréville, 1964;Baehni, 1965;Pennington, 1991): depending on the weight given to one or the other character, classification and number of accepted genera can change drastically. Those discrepancies do not allow conservation action to rely on strong taxonomic data. Thanks to molecular studies (e.g. Anderberg & Swenson, 2003;Swenson & Anderberg, 2005), nomenclatural stability is at hand and current efforts aim at revising this economically important and threatened family worldwide. In the Flore de Madagascar et des Comores (Aubréville, 1974), the Sapotaceae family was represented by 11 genera and 84 species. The abundant material accumulated since clearly indicates the need of re-evaluating the taxonomy of this family for Madagascar, with the help of appropriate molecular methods. Numerous new taxa are suspected, some of them having been already described (e. g. Gautier et al., 2013;Mackinder et al., 2016;Gautier & Naciri, 2018).
The Sapotaceae genera present in Madagascar belong to the two main subfamilies: Chrysophylloideae (with the genera Donella Pierre ex Baill. and Gambeya Pierre), but mainly to Sapotoideae. Within Sapotoideae, three tribes are represented: Sideroxyleae (with Sideroxylon L.), the recently described endemic Tsebonae (Gautier et al., 2013) (with Bemangidia L. Gaut., Capurodendron Aubrév., and Tsebona Capuron) and Sapoteae (with Mimusops L., Faucherea Lecomte, Labourdonnaisia Bojer, Labramia A. DC., and Manilkara Adans.). The four latter genera belong to the subtribe Manilkarineae (Pennington, 1991) which is characterized by a calix arranged in two whorls of three sepals. A recent molecular study on the genus Manilkara worldwide (Armstrong, 2010) including a restricted sample of Faucherea, Labourdonnaisia and Labramia pointed out that the relationships between these three genera are not well-resolved. As currently accepted, Faucherea is endemic to Madagascar, Labourdonnaisia being shared with the Mascarene Islands, and Labramia with the Comoros. Aiming at establishing conservation action based on strong taxonomic data, we undertook molecular studies and in-depth morphological analyses on a large sample of Faucherea, Labourdonnaisia and Labramia species, to investigate the generic circumscriptions and to solve species delimitations within this group. The three genera have many features in common. However, Labramia clearly differs by the presence of a pair of dorsal appendages to the corolla lobes, a glabrous ovary, and seeds with a lateral scar almost as long as the seed. It is considered by Pennington (1991) as a "well-knit group of […] species". Moreover, it appears as a well-supported monophyletic clade according to previous molecular study (Armstrong, 2010). Our analyses based on an extended sampling and numerous nuclear genes give congruent results (Randriarisoa et al., unpubl. data).
There are currently nine known species of Labramia, among which eight are endemic to Madagascar (Gautier, 2003) and one to the Comoros (Labat & Pascal, 1997). In Madagascar, the geographical distribution of the genus extends mainly along the dense humid evergreen forest of the Eastern Domain (Humbert, 1955), but with one species found in the karstic limestone massifs in the West and the North. While revising the herbarium specimens of all Labramia species, many specimens could not be identified with confidence using the treatment of Aubréville (1974). Among the material sorted as potential new species to be described, it was obvious that a Labramia collection from the littoral forest in the Northeastern coast clearly differed from all other specimens. Taking into account its rarity, the fragility of the habitat of its single known location (Consiglio et al., 2006), and its clear morphological differences from other Labramia species, we propose here its formal description, anticipating the results of ongoing molecular studies which will ultimately provide a complete taxonomic revision of the genus. The new species is provided with a line drawing and its risk of extinction assessment using the IUCN Red List Categories and Criteria (IUCN, 2012).

Holot y pus
Tree (dimensions unknown), with white latex. Ultimate twigs 2 mm diameter, glabrous, brownish, with pales lenticels, soon becoming greyish and longitudinally ridged. Leaves alternate, petiole 10 -15 × 1.1 -1.6 mm, glabrous, with a median groove on upper side in continuation of the primary nerve; blade cuneiform, the widest portion 1/4 from the top and decreasing almost regularly to the acute base, apex rounded to slightly emarginated; (30 -)40 -65( -70) × 15 -30 mm, entirely glabrous even when young, drying brown and discolours, darker above. Primary nerve prominent below, depressed above; secondary venation inconspicuous on upper side, visible on lower side, 10 -12 pairs of secondaries, ascending with an angle of c. 30° -40°, straight and parallel to each other until their connexion through a marginal nerve 0.9 mm from the margin; intersecondaries present; tertiary venation faint. Flowers 1 -3, fasciculate, borne axillary to the current year's leaves or above the scar of previous year's fallen leaves; flowering pedicels 12 -15 × 0.6 -0.8 mm, broadening to c. Etymology. -This species epithet refers to the name of the village of Ambondrombe, near the littoral forest where the type specimen was collected.
Phenology. -The flowering specimen was collected in March.
Distribution and Ecology. -Labramia ambondrombeensis is only known from the type collection in Northeastern Madagascar, at the extreme North of the Eastern Phytogeographic Domain, near the southern limit of the Northern Sector of the Western Domain (Humbert, 1955). It was collected in a littoral forest on sands.
Conservation status. -The new species is known only from a single location in a little patch of unprotected littoral forest. Littoral forest is under major threat of logging and habitat conversion (Consiglio et al., 2006). With only one known location and an AOO of 4 km2, outside of the protected area network, L. ambondrombeensis is assigned a provisional status of "Critically Endangered" [CR B1ab(i,ii,iii)+2ab(i,ii,iii)] using the IUCN Red List Criteria (IUCN, 2012).
Notes. -Labramia ambondrombeensis is clearly distinct from most other Labramia species because of its small leaves (4.0 -6.5 cm long). The only other species, also occurring in the North of Madagascar, with such small leaves is L. platanoides Capuron ex Aubrév. Apart from the morphological distinctions, habitat preferences distinguish the two species: while the specimen of Labramia ambondrombeensis was collected in littoral forest on sand, Labramia platanoides is known to have a predilection for dry deciduous to semi-deciduous forests on limestone (Aubréville, 1974). Labramia ambondrombeensis is not the only species in littoral forest; further south, under per-humid climate, one finds L. bojeri with much larger leaves (up to 25 cm long).