Research Article |
Corresponding author: Gildas Gâteblé ( gildas.gateble@inrae.fr ) Academic editor: Laurence J. Dorr
© 2018 Gildas Gâteblé, Jérôme Munzinger.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Gâteblé G, Munzinger J (2018) Novitates neocaledonicae X: A very rare and threatened new microendemic species of Acropogon (Malvaceae, Sterculioideae) from New Caledonia. PhytoKeys 110: 1-8. https://doi.org/10.3897/phytokeys.110.27599
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A new species, Acropogon horarius Gâteblé & Munzinger, sp. nov. (Malvaceae, Sterculioideae), is described from New Caledonia. It is known only from two very small subpopulations in the rainforests of the Petchécara Pass between Thio and Canala, in the southeast of Grande-Terre, New Caledonia’s main island. This shrub to small tree has hastate leaves and minute sessile tubular whitish-yellowish flowers and is strikingly different from all other members of the genus. The type locality is geologically complex and located within one of only four amphibolite lenses known in New Caledonia. A line drawing and colour photos are provided for the new species, along with a preliminary risk of extinction assessment, which indicates that the species is Critically Endangered.
Acropogon , geology, Malvaceae , New Caledonia, new species, Sterculioideae , taxonomy, threatened species
The endemic New Caledonian genus Acropogon Schltr. (Malvaceae, Sterculioideae) comprises 26 currently recognised species (
In this paper, we describe and illustrate a morphologically distinctive new Acropogon species. We also provide a risk of extinction assessment based on the IUCN Red List Categories and Criteria (
Distribution of Acropogon horarius Gâteblé & Munzinger sp. nov. mapped on the geological (A) and soil (B) GIS layers of the Petchécara Pass. Insert A, geology from
In order to determine whether the material from the Petchécara Pass belonged to a currently recognised species or represented a new member of the genus, we carefully examined and measured living specimens and herbarium material. We focused on morphological characters recognised by previous authors (
Acropogon horarius Gâteblé & Munzinger differs from all other members of the genus by the combination of its long and thin petioles, hastate and cordate leaves and minute sessile tubular whitish-yellowish flowers.
New Caledonia. Province Sud: Thio, Col de Petchécara, route à horaire, 200 m alt., 21°34'41.01"S, 166°07'22.41"E, 25 Aug 2016, G. Gâteblé, J. Ounémoa, M. Moenteapo & E. Poitchili 806 (holotype: P00722668; isotypes: K, MPU311373, NOU088956, P00722670).
Acropogon horarius Gâteblé & Munzinger sp. nov. A flowering branch B inflorescence and a zoom on stellate trichomes of the flower tube C female flower D male flower E infructescence F detail of erect stellate trichomes on the follicle’s surface G detail of an open follicle H close-up of the abaxial leaf reticulum. Drawings by Laurence Ramon (A–H Gâteblé et al. 806).
Monoecious shrub to small tree up to 6 m tall, sparsely branched with usually a main trunk less than 7 cm in d.b.h.; bark brown, with conspicuous scars left by the caducous cataphylls and sometimes petioles of upper leaves subtending the terminal bud. Leaves clustered at the apex of branches on adult plants, branches 4–5 mm in diameter; petioles light green to yellow (greyish to orange in herbarium material), strongly different in colour than the branch, glabrous, (6.5–)9.0–12.0(–15.5) cm long, 1–2 mm in diameter, elliptical in cross section (in vivo), slightly striate (in herbarium material), enlarged (3–4 mm) proximally and distally, the pulvini slightly pruinose (in vivo); blades simple, coriaceous, flat, slightly discolorous, glabrous on both surfaces, unlobed to slightly hastate on juvenile plants (Gâteblé et al. 804), rarely unlobed to strongly trilobed or hastate on adult plants, (10.5–)12.5–15.0(–16.0) cm long, (6.0–)11.5–18.0(–23.5) mm wide, base cordate (rarely truncate), apex of the lobes broadly acute to rounded; generally with 3 strong primary palmate veins, primary and secondary veins prominent abaxially, conspicuously different in colour (yellow-orange in herbarium material and light green to yellowish in vivo) than the blade, reticulum visible abaxially (and adaxially in herb.), secondary veins 2–5 pair; tertiary and quaternary veins finely reticulate with scattered crateriform glands 25–35 µm. Inflorescence a reduced spike-like raceme, axillary within, above or just below the terminal cluster of leaves, up to 3.5 cm long, 2.5–3.5 mm in diameter, axes greenish-yellowish, covered with a dense rust-brown indumentum composed of minute stellate trichomes ca. 90 µm x 90 µm, bracts covered with rust-brown tomentum adaxially. Pedicels minute. Male and female flowers seemingly randomly distributed within the inflorescence, solitary, of the same size. Calyx tubular, 4–5 mm long, 2–2.5 mm in diameter, yellowish and with scattered rust-brown stellate trichomes outside, whitish and glabrous inside, lobes 5, triangular, 1–1.5 mm long, ending in an apical appendage 0.5–1 mm long, interior margins of the lobes and appendages covered with papillose glandular trichomes 35–55 µm long, 15–20 µm in diameter. Male flowers: androecium ca. 4 mm long; androphore tubular, ca. 2 mm long, 0.7–1 mm in diameter, with a few scattered glands; stamens 6–8, ca. 1.7 mm long, inserted at apex of androphore; anther dehiscence longitudinal, extrorse. Female flowers: gynophore ovoid, ca. 1 mm in diameter, with a few scattered glands; staminodes 5–7, composed of sessile, sterile anthers, ca. 1.3 mm long, inserted at the base of the gynophore; ovary ovoid, 1.5–2 mm in diameter, with 3–4 carpels, covered by a dense indumentum of stellate trichomes; style ca. 1 mm long, with scattered stellate trichomes; stigmas 3 or 4 ovoid, 0.4–0.5 mm long. Infructescence 7–12 cm wide, borne on a peduncle 0.5–3 cm long, 2.5–3.5 mm in diameter. Fruit comprising 1–4 follicle(s), each borne on a pedicel 0.5–0.8 cm long, 0.2–0.3 cm in diameter at maturity, green and turning greenish-yellow towards maturity, covered by sparse, erect, stellate trichomes, each follicle ellipsoid to ovoid, 3.5–4.5 cm long, 2.5–3 cm wide, with a woody pericarp ca. 0.2 cm thick in dry material (ca. 0.3 cm in alcohol), apex apiculate. Seeds 4–6 per locule, ellipsoid, white when immature, light brown to black at maturity, 10–12 × 4–6 mm in diameter.
The new species is only known from the south-eastern part of the Grande-Terre, at the Petchécara Pass between Thio and Canala (Fig.
Young plantlets of Acropogon horarius are fairly easy to grow in nursery conditions. Shrubs have been grown in a private nursery (Eriaxis nursery) and at the research station of Institut Agronomique néo-Calédonien located in Saint-Louis, Mont-Dore.
The plant is named after the last of New Caledonia’s scheduled roads or “route à horaire” along which it grows.
With its hastate and cordate leaves and its long and thin petioles, its minute sessile tubular whitish-yellowish flowers, Acropogon horarius cannot be confused with any other member of this endemic genus. In fact, the morphological characters of its inflorescence [reduced spike-like raceme of solitary (sub)sessile flowers versus true racemes and panicles in other species] and flowers (tubular versus cup shaped in the other taxa) appear to be unique in the genus. A phylogenetic study would be worthwhile to determine whether A. horarius belongs to a distinct clade within the genus. The very slow development of the inflorescence axis (or brachyblast), which takes several months, is also unusual as it appears to produce flowers sequentially throughout its growth, perhaps until there is a successful fruit set or until the axis becomes too long (3.5 cm) to produce more flowers, as opposed to the much more nearly synchronous flowering in all other species. The combination of a prolonged duration of flowering and the unusual morphology of the minute tubular flowers suggests that the breeding mechanism in A. horarius may be different from that of other members of the genus.
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NEW CALEDONIA. Province Sud: Thio, Col de Petchécara, route à horaire, 200 m alt., 21°34'41.01"S, 166°07'22.41"E, 25 Aug 2016, G. Gâteblé, J. Ounémoa, M. Moenteapo & E. Poitchili 805 (MPU311374, NOU088958, P00722669), Ibid., 270 m alt., 21°34'36"S, 166°07'28"E, 25 Aug 2016, G. Gâteblé, J. Ounémoa, M. Moenteapo & E. Poitchili 804 (NOU088959, P00722672), Ibid., 25 Aug 2016, G. Gâteblé, J. Ounémoa, M. Moenteapo & E. Poitchili 803 (K, MEL, MPU311375, NOU088960, P00722671), Ibid., 200 m alt., 21°34'41.01"S, 166°07'22.41"E, 3 Aug2017, G. Gâteblé & J. Taramoin 981 (MO, MPU311376, NOU088957, P00722674).
We thank Jean-Jacques Villegente and Jacqueline Ounémoa, who first noticed the new species in the field and Jacqueline Ounémoa, Joanney Taramoin, Michel Moenteapo and Edmond Poitchili for enthusiastic help spotting plants in the forests of Petchécara Pass. We are grateful to the team at the NOU herbarium (IRD, Nouméa) and Jacqueline Tinel and Giliane Karnadi-Abdelkader, for mounting and computerising the specimens, Laurence Ramon for providing the fine illustration of Figure