Pseuderanthemum melanesicum Gateble , Ramon & Butaud, 2019

Gateble, Gildas, Ramon, Laurence & Butaud, Jean-Francois, 2019, A new coastal species of Pseuderanthemum (Acanthaceae) from Loyalty Islands (New Caledonia) and Vanuatu with notes on P. carruthersii, PhytoKeys 128, pp. 73-84 : 73

Pseuderanthemum melanesicum Gateble, Ramon & Butaud sp. nov. Figs 1 , 2 , 3

Diagnosis.

Pseuderanthemum melanesicum Gâteblé, Ramon & Butaud is most similar to some cultigens of P. carruthersii but differs from them by its carnose leaf texture vs. chartaceous, by its pedicels and sepals with glandular hairs vs. eglandular hairs, by its glabrous petals and tube vs. hairy petals and tube and by its short and enlarged corolla tube vs. longer cylindrical corolla tube.

Type.

NEW CALEDONIA. Province des Iles Loyauté: Lifou, plant cultivated at the Agricultural Research Station Saint Louis at Mont-Dore , 4 December 2018, G. Gâteblé 1072 (holotype P; isotypes NOU [NOU089981, NOU090339]) .

Description.

Fruticulose shrubs up to 1.5 m tall, generally decumbent to somehow erect, somewhat carnose. Branches round (living material) to angulate (dry material) in cross section, beige to brown on older stems, pale green on young stems; prominent leaf and bundles scars; lenticels few, glabrous. Leaves simple, opposite-decussate, usually ovate to broadly elliptic, rarely obovate; blade (7-) 8-11 (-12) × (2.5-) 5-6 (-6.5) cm, vernicose, carnose, glabrous on both surfaces; apexes obtuse to rounded, sometimes slightly retuse or acuminate, bases cuneate to attenuate, margins entire; midveins slightly impressed adaxially, prominent abaxially toward the base, glabrous; secondaries of 4-6 opposite or alternate veins, more or less brochidodromous; tertiaries in a loose reticulum; petioles (0.5-) 1-1.5 (-2.5) cm long. Inflorescences terminal, a raceme or panicle, 1-12 cm long; rachises round to quadrangulate in cross section, mostly glabrous but with some glandular hairs in its most apical part; peduncles 1-5 cm long usually glabrescent but sometimes with some glandular hairs; bracts and bracteoles lanceolate 1-4 mm × 0.5-1.5 mm, glabrescent to piloglandulose. Flowers bilaterally symmetrical; pedicels 3-11 mm long, piloglandulose. Sepals 4 or 5, lanceolate, 3.5-4 × 1 mm, piloglandulose on the outer surface, glabrescent inside. Corollas ampliate to slightly ventricose, white with purple center, aestivation imbricate in bud; tubes ca. 1-1.3 cm long, glabrous, enlarged distally to 3-5 mm diameter before the throat, 4-5 lobed, consistently three in the lower half, and one or two in the upper half; lobes elliptic, 5-8 × 4-7 mm, the lower one being the larger, glabrous. Stamens 2, slightly exserted, inserted in the tube orifice on to the upper lobe(s), filaments 4-4.5 mm long, glabrous, anthers ca. 1.8 × 0.8 mm; staminodes 2, ca. 1 mm long. Ovaries conical, 4.5 × 2 mm, glabrous; styles slightly exserted, ca. 15 mm long, glabrous; stigmas bilobed, lobes ca. 0.5 × 0.15 mm. Fruits stipitate dehiscent capsules, clavate, 1.5-3 × 0.6-0.8 cm, sometimes crowned with the remnant style; seed (4-?) per capsule, ovate, 3-4 mm × 2-3 mm.

Distribution and ecology.

In New Caledonia and Vanuatu, P. melanesicum is found in coastal thickets on limestone substrate, either coastal reef, cliffs or back of the beaches, with species of Bikkia Reinw. ex Blume, Dendrolobium (Wight & Arn.) Benth., Eugenia P.Micheli ex L., Heliotropium Tourn. ex L., Hibiscus L., Myoporum Banks & Sol. ex G.Forst., Nicotiana L., Pemphis J.R.Forst. & G.Forst., Sarcolobus R.Br. and Xylosma G.Forst. at 2-60 m elevation in the Loyalty Islands. In New Caledonia, it is only known from Lifou and Maré in the Loyalty Islands and it is known from Efaté and Malakula in Vanuatu (Fig. 1 ). With such a distribution, the species should be more common than reflected by the available herbarium specimens. Recently (February 2019) the species was seen in relatively large populations on Erakor Island (Port Vila) and Port Resolution (Tanna). Like in other Acanthaceae , P. melanesicum seeds are dispersed through ballochory that could explain the many individuals found in some populations in Vanuatu. The seed seems also able to float on sea water for a few hours (observation made with only one seed).

Etymology.

The new species is named after the Melanesian archipelagos of New Caledonia and Vanuatu.

Species recognition.

With its carnose and shiny leaves (especially seen on fresh material), its short and broaden corolla tube and its many glandular hairs on pedicels and sepals, P. melanesicum is easily separated from the cultivated, widespread and variable taxon, P. carruthersii . In addition, in both countries the new species has been collected in fruit while there is, to our knowledge, no fruiting specimen of P. carruthersii in the region. The well-known south-western Pacific botanical specialist Peter Shaw Green (1920-2009) also thought it was a putative new species as he wrote " Pseuderanthemum sp.? ined" on several herbarium sheets (e.g., Hallé 6331 and Gillison 3539).

Notes.

Color figures of P. melanesicum have already been published twice under misapplied names of other species inhabiting Loyalty Islands and Vanuatu, once as P. repandum (G.Forst.) Guillaumin subsp. loyaltyensis (Guillaumin) Heine or «Waditcha» in Suprin (2008: 177), and the other one (fig. 119a) as P. carruthersii in Ramon and Sam (2015: 121). The vernacular name Watija in Maré can be related to P. repandum subsp. loyaltyensis but this name was not recorded recently ( Lormée et al. 2011) for that species; Watija is clearly the local name of Psychotria nummularioides Baill. ex Guillaumin and has also been given to Cleidion verticillatum Baill., a shrub of the same size (Butaud, pers. obs.). Two local names are reported on Gillison 3539 for Vanuatu as Nuguvere and Malandi . According to Gâteblé et al. (2018), P. melanesicum is only the third non-endemic species described from New Caledonia since the beginning of the 21st Century. Pseuderanthemum melanesicum is easily propagated by cuttings and it thrives well in cultivation. Even in cultivation, the carnose and shiny leaves are maintained (Fig. 3 ) and it makes a nice native ornamental plant for gardens and landscaping in open or shaded areas.

The cultivated plant from which the type specimen was prepared was originally collected by J.-F. Butaud on Lifou, north of Wé to Luecila, (2 m elevation, 20°53'34.56"S, 167°16'18.56"E) on 19 April 2014.

Preliminary conservation status (IUCN 2017).

In New Caledonia, the species is very uncommon and was collected only recently from the east coasts of Lifou and Maré islands. Recently 15-20 shrubs were seen on Lifou and two on Maré but B. Suprin (pers. comm., 2015) states he has seen it in a few places on Maré and Lifou. On Maré, the species is threatened by feral goats that seem to graze young stems and that contribute to habitat degradation. On Lifou, in its only currently known location, the species is not clearly threatened; the only threats could come from agriculture as nearby areas are cultivated. The distribution of P. melanesicum in New Caledonia is similar to that of Cyrtandra mareensis Däniker but much rarer for the number of individuals. Its area of occupancy is 8 km2 while its extent of occurrence is less than 500 km2. It is considered severely fragmented as each subpopulation could go extinct with a very reduced probability of natural recolonization from the other subpopulation. A continuing decline has been observed and/or estimated for its quality of habitat and number of mature individuals. Based on the IUCN Red List Categories and Criteria ( IUCN 2017) and using criteria B, P. melanesicum qualifies for Critically Endangered CR B2ab(iii,v) in New Caledonia. Using criteria D, with less than 50 individuals, P. melanesicum qualifies also for Critically Endangered (CR D). In Vanuatu, this species is commonly observed on Efaté island’s seashore and the major threats are forest and coastal clearing for housing on private properties (e.g. in Havannah and Undine bays and south from Eton village). The recently seen Erakor Island ( Efaté) population is also facing disturbance due to the resort while the Port Resolution (Tanna) population is not facing major threat. No threat has been identified on Malakula and the species should also be present on other southern islands (Ambrym, Epi, Erromango and Aneityum) of the archipelago of Vanuatu towards the Loyalty Islands with no major associated threat. As a putative common species in Vanuatu with between five to ten locations and with threats only in the south of Efaté, the species could qualify as VU B2ab(ii,iii,v). Globally, for both New Caledonia and Vanuatu, P. melanesicum could be considered as Least Concern against IUCN criteria because of there being more than ten putative locations and both the extent of occurrence and area of occupancy are above the threshold for assessment of a threatened category using criterion B.

Additional specimens examined.

NEW CALEDONIA. Province des Îles Loyauté: Lifou, Luecila, 2 m, 20°53'34.56"S, 167°16'18.56"E, 15 April 2015, J.-F. Butaud 3427 (NOU [NOU090338]); plant cultivated at the Agricultural Research Station Saint Louis at Mont-Dore, 13 May 2015, G. Gâteblé 679 (NOU [NOU089984]); ibid. loc., 7 December 2015, G. Gâteblé 722 (NOU [NOU089982, NOU089983]); ibid. loc. 29 December 2015, G. Gâteblé 740 (NOU [NOU089985, NOU090341]); ibid. loc. 19 February 2019, G. Gâteblé 1073 (NOU [NOU090340]). Maré: Sentier littoral entre Eni et Shabadran, 60 m, 21°39'25.57"S, 168°0'22.45"E, 2 April 2018, G. Gâteblé, Drouin J, Jewine A. & Wamejongo W 1024 (MPU, NOU |NOU089986], P, K, LOY) . VANUATU. Efaté, Eton , plage privée (avant le blue hole), 0 m, 17°45'0.55"S, 168°33'55.46"E, 5 August 2015, L. Ramon 220 (NY [NY03487104], P [P02434405], PVNH). Malekula, Tisbel, 29 September 1971, N. Hallé 6331 (NOU [NOU077567], P [P04385831]); ibid. loc., 28 September 1971, A.N. Gillison 3539 (P [P04385834]) .

Figures

Figure 1. Distribution of Pseuderanthemum melanesicum Gateble, Ramon & Butaud, sp. nov. in some islands of New Caledonia and Vanuatu. Map done using CartoGIS Services, College of Asia and the Pacific, The Australian National University.

Figure 2. Drawings of Pseuderanthemum melanesicum Gateble, Ramon & Butaud, sp. nov. and P. carruthersii A-G Pseuderanthemum melanesicum H-I Pseuderanthemum carruthersii A, D Structure of the inflorescence B Flower C Flower bud E Open corolla with the lower corolla lobe removed to show the arrangement of internal structures F Open mature and immature capsules G Glandular hairs on a flower bract H Eglandular hairs on the outer surface of the corolla tube I Part of inflorescence showing the long narrow tube of a flower. Voucher specimens: A-D Gateble 1072 E, G Gateble 722 F Ramon 220 H-I Gateble 720. Drawings by Laurence Ramon.

Figure 3. Field pictures of Pseuderanthemum melanesicum Gateble, Ramon & Butaud, sp. nov. and P. carruthersii A-D. Pseuderanthemum melanesicum E-F Pseuderanthemum melanesicum and P. carruthersii A Overview of a single shrub hanging from a coastal limestone cliff on Mare island B Flowering branch on Efate island C Flower D Infructescence and ecology on Lifou island E Cultivated plants of P. carruthersii (left) and P. melanesicum (right) F Leaves and inflorescences of P. melanesicum (left) and two cultigens of P. carruthersii (center and right). Photographs by G. Gateble (A, C, E-F), L. Ramon (B) and J. - F. Butaud (D); Voucher specimens: A Gateble et al. 1024, B Ramon 220, C Gateble 722, F Gateble 722, 721, 720.