Heterostemma bicanthaceum Meve, Gateble & Liede. A 2018, sp. nov.
Creators: name: Meve, Ulrich
name: Gâteblé, Gildas
name: Liede-Schumann, Sigrid
Publisher: name: Zenodo
Year: 2018
Subjects: Biodiversity
Taxonomy
Plantae
Tracheophyta
Magnoliopsida
Gentianales
Apocynaceae
Heterostemma
Heterostemma bicanthaceum

description: Heterostemma bicanthaceum Meve, Gâteblé & Liede, sp. nov. (Fig. 1A, B; 2 and 3)   
 TYPE: New Caledonia, Ile des Pins, Gadji, 5 m, Mar 15, 1972, H. S. MacKee 25158 (leg. P. Lecureuil) (holotype P 04237467, P).   
 Diagnosis: In habit like Heterostemma acuminatum Decne. but differing in the shape of the corolla tube that is slightly arching upwards centrally to embed the margins of the gynostegium (cv. corolla tube flat in H. acuminatum with the gynostegium sessile and in the same plane as the tube); the purplish brown corona with dull and uneven, bullate to wrinkled surfaces (vs. purple red, rather smooth surfaces in H. acuminatum ); possessing expanded lateral coronal appendages that are touching each other laterally to form an external, additional guide rail (vs. wing-like appendages that leave much free space in front of the guide-rail in H. acuminatum ); and a pollinium that is only 0.13 mm long (vs. 0.25 mm in H. acuminatum ).   
 Plants ascending and twining to 3–4 m high. Shoots perennial, herbaceous, basally corky, glabrous; internodes to 15 cm long, 1.5–10 mm diam. Latex colorless. Leaves spreading, petiole 40–50 mm long; base of leaves with 9–14 colleters; blades herbaceous, 7–10 x 4–9 cm, ovate or broadly elliptic, basally cordate, apically acuminate to acute, adaxially dark green, abaxially (bright) green, glabrous on both sides except for scattered trichomes on the nerves. Inflorescences one per node, extra-axillary, with one basal dichotomy supporting two sciadioids, 4–12-flowered, 1–4 flowers open synchronously. Peduncles 15–30 mm long, glabrous or nearly so. Bracts pointedly ovate, c. 1.5 mm long, pilose with brownish, multi-cellular trichomes. Flowers spreading. Pedicels 10–12 mm long, glabrous to sparsely covered with appressed, 150 μm long trichomes. Calyx basally fused, sepals 1–1.5 x c. 1 mm, triangular-deltate, apically obtuse, abaxially pilose on central parts. Corolla rotate-subcampanulate, 10–12 mm in diam, fused for a quarter of length, bright yellowish green, glabrous; corolla lobes spreading, triangular, 4.5–6 mm long, 2.5–3 mm wide, apically acute, tips slightly revurved, corolla tube c. 5 mm diam., centrally slightly raised to embed the margins of the gynostegium. Gynostegial corona purplish brown except for lower bright green margins, glabrous, 2–2.5 mm diam. in total, staminal corona tripartite with a distal triangular lobule, c. 0.4 mm long, 0.5 mm wide at base, pointed, incurved on style-head; median staminal corona lobules slightly overtopping the gynostegium in length, c. 1 mm long, erect, solid, oblongoid, digitate or hooked, and proximal staminal corona lobule inconspicuous or knob-like, 0.1–0.4 mm wide, fleshy, emarginate, occ. pointed, surface uneven to wrinkled; staminal corona additionally with two lateral subrectangular appendages each, c. 0.7 mm long, 0.4 mm wide, smooth, with their margins laterally touching each other along the whole length to form a “coronal guide rail” (prepending to the gynostegial guide-rails), usually forming a “mouth”. Gynostegium 1.4–2. mm in total length, 2 mm diam., basal third embedded in corolla tube; anthers c. 0.5 x 0.5 mm, rectangular; anther wings of adjacent anthers parallel to each other, c. 200 μm long, anther appendages reniform, c. 0.2 x 0.5 mm. Pollinarium: erect, touching top of style-head, corpusculum c. 110 x 40 μm, ellipsoid-deltoid; caudicles c. 40 μm long, centrally attached to the corpusculum, flattened, straight, linear; pollinia baseo-laterally attached to the caudicles, suberect, c. 125 x 250 μm, germination crest lateral along inner sides, c. 0.1 mm long, number of pollen grains per pollinium around 54. Style-head conical, c. 0.5 mm long, 1 mm diam., solid. Follicles normally two per flower, in an angle between almost 90° to 180°, 10–15 cm long, 5–8 mm wide, slenderly fusiform, round in cross-section, apically beaked, wingless, shiny green when young, dull bright brown with maturity, smooth, glabrous, with thin pericarp; number of ovules per ovary 8–10. Seeds 10–12 x 6–7 mm, ovate, light brown; smooth on both sides; marginally with 0.3–0.4 mm wide wing, laterally with entire margin, apically with dentate margin; coma 30–40 mm long.   
Distribution and habitat: New Caledonian endemic (Grande Terre, Ile des Pins). In the calcareous rocks of Koumac and on Kuébini peninsula south of Yaté on Grande Terre and Ile des Pins—Coastal-near gallery forests, moist primary forests, calcareous rocky soil; 5– 50 m.  
 Phenology: (fig. 3) Flowers: December, March, April. Fruits: March, July, October, November.   
 Provisional IUCN Status: The endemic Heterostemma bicanthaceum is restricted to the calcareous mesic to moist forests of Ile des Pins, Kuébini and Koumac. The species is probably already extinct in the Koumac calcareous rocks because of high habitat degradation due to invasive deer (Rusa timorensis). As already reported in Munzinger & Gâteblé (2017), mesic forests of west Grande Terre face severe degradations due to deer overgrazing and soil erosion. The species is not rare on Ile des Pins but it is localized only in the richest and the best preserved parts of the forests. The threats are quite low on Ile des Pins with a few feral pigs (Sus scropha) and low logging in the Gadji area. The state of the Kuébini population is not known. Considering the fact that the biogeographically important Koumac population is severely threatened or probably extinct, we propose the “Endangered” (EN) IUCN (2017) category under the criterion B 1ab(i,ii,iii,iv,v)+2ab(i,ii,iii,iv,v).   
Etymology: The name refers to doubly occuring rail structures.Apart from the usual guide rails of the gynostegium formed by the margins of the stamens, a second prepending rail-like structure occurs, composed by the specific lateral appendages of the staminal corona lobes.  
 Remarks: The new species is most conspicuously characterized by rail-like structures prepending the gynostegial guide-rails, that are composed of extended lateral appendages of the staminal corona lobes. Their function is unknown. Possibly they play a role in guiding the flower visitors, or in securing nectar against illegitimate flower visitors. A comparable secondary structure is not known from other Heterostemma species, however, it is characteristic for quite a number of species belonging to the South American genus Tassadia (Decaisne 1844: 579) (Asclepiadeae-Tassadiinae), e.g. Tassadia guanchezii (Morillo) Liede & Meve (Liede & Meve 2015: 40, Fig. 2 C, D).   
Paratypic material:  
 Grande Terre: North Prov., Koumac: Tchabel, 30 m, Dec 27, 1966, MacKee 16197 (NOU017789, NOU; P04237468, P); South Prov., Kuebini, Ile Nou, 2 m, Oct 29, 1970, MacKee 22807 (NOU017788, NOU; P04237466, P).   
 Ile des Pins: Sentier entre Baie d´Oro de Baie d´Upi, 13 m alt., Apr 20, 2016, Gâteblé, Karnadi & Laudereau 756 (UBT, in alc.); Ilots Ouate et Koungouati, Oct 13, 1966, MacKee 15833 (NOU057761, NOU); Gadji, 5 m, Jul 22, 1970, MacKee 22291 (NOU017787, NOU; P04237469, P); Gadji, vers la scierie, Feb 02, 1966, Nothis 299 (NOU057760, NOU); Jul, 1909, Le Rat 123 (P04237470, P); secteur de Oupi, Jun 11, 1967, Schmid 2065bis (NOU017786, NOU).
description: Published as part of Meve, Ulrich, Gâteblé, Gildas & Liede-Schumann, Sigrid, 2018, Two new species from the Ile des Pins (New Caledonia), and a not so new species from Grande Terre (New Caledonia), pp. 201-213 in Phytotaxa 349 (3) on pages 202-205, DOI: 10.11646/phytotaxa.349.3.1, http://zenodo.org/record/13709257