Citronella hirsuta Munzinger, 2016

Munzinger, Jérôme & Levionnois, Sébastien, 2016, Novitates neocaledonicae III: A new species of Citronella (Cardiopteridaceae) endemic to New Caledonia, Phytotaxa 245 (3), pp. 223-228 : 225-227

Citronella hirsuta Munzinger , sp. nov. ( Figs. 1A , 2 & 3 )

Type:— New Caledonia. Province Nord: Route Poro-Kouaoua, 21°22’24”S, 165°44’07”E, 17 December 2006, J. Munzinger, D., I. & C. Létocart 4045 (Holotype P 00641022, Isotypes MO, MPU 026671, NOU 017285).

Diagnosis:—The new species resembles Citronella sarmentosa in lacking domatia on the abaxial surface of its leaves, in forming small shrubs, and in having terminal, erect inflorescences, but can be distinguished by the dense, persistent hirsute indument on its leaves, petioles and inflorescences axes, versus glabrous leaves and petioles, and short, appressed trichomes on the inflorescences axes in C. sarmentosa .

Shrub, up to 3 m tall, multi-stemmed. Bark dark brown. A hirsute indumentum of orange/golden trichomes ~ 0.5 mm long present on leaves, petioles, and inflorescences. Leaf blades homomorphic, 7–13 x 2–5 cm, lanceolate to ovate or oblong, base usually asymmetric, rounded to cuneate, margin revolute, apex acuminate, sometimes weakly so, abaxial surface densely pubescent, adaxial surface less so, midvein strongly convex on abaxial surface, concave on adaxial surface, secondary veins 4–7. Petiole canaliculate, pubescent, 7–10 (–15) mm long.

Inflorescence a raceme of scorpioid cymes, 3–20 cm long, axillary and terminal. Cymes 3–15 mm long, bearing up to 12 flowers. Bracts triangular, 1 x 0.5 mm, with black trichomes. Peduncle pubescent. Floral buds obovate, 3–4 x 1.5–2 mm. Flowers pentamerous, bisexual. Sepals imbricate in bud, white, glabrous on both surfaces, 0.5–1.5 x 0.5–1 mm, united at the base, margin usually ciliate with 0 to 5 long, orange/golden trichomes ~ 0.5 mm long. Petals valvate 2/3 of their length and imbricate at summit in bud, oblong, glabrous on both surfaces, white/light yellow to dark brown when dry, apex of each petal twisted, 1.5–3 mm long, base 0.5–1 mm wide, distal half 1–2 mm wide, early caducous. Stamens 5, glabrous, filaments 2–3 mm long, anthers ~ 1 mm long. Gynoecium glabrous, conical, ovary 0.5 x 1.5 mm, style 1.5–2.5 mm long, stigma two-lobed, blackish (in herb.). Fruit a drupe, 1–2 x 0.5–1 cm when dry (in herb., only immature known), ellipsoid, glabrous, dark brown/black when dry (in herb.). Seeds not seen.

Phenology:—Flowers of Citronella hirsuta have been observed in December and February, and immature fruits have been collected in April.

Distribution and Ecology:—This new species is only known from the east-central part of New Caledonia’s main island, Grande Terre, in North Province ( Fig. 3 ), where it occurs in thalweg (gully) forest and dense maquis vegetation on ultramafic substrate, at around 200 meters elevation. Only five adult individuals are known but intensive field prospection in the area could potentially locate other individuals.

Etymology:—The plant is named based on the unique nature of its indumentum among New Caledonian Citronella species.

Species recognition:—Even sterile, individuals of Citronella hirsuta can easily be distinguished from its New Caledonian congeners by its unique hirsute indument of orange/golden trichomes found on the leaves, including both the petiole and blade, as well as the inflorescence. Citronella hirsuta also differs from C. macrocarpa by lacking domatia on the abaxial surface of its leaves, and the fact that it is a small shrub, rather than always having at least one domatium in the axil of a secondary vein where it joins the midvein (and sometime also between secondary and tertiary veins), and in being a large tree up to 40 cm in diameter that has been exploited for its wood (in Sarlin 1954, confused with C. sarmentosa at that time; C. macrocarpa was published 10 years later). All three New Caledonian species of Citronella have indument on their inflorescences but in C. sarmentosa and C. macrocarpa the trichomes are scattered and appressed ( Fig. 1B, C ), whereas in C. hirsuta they are numerous and erect ( Fig. 1A ). Moreover, C. sarmentosa and C. hirsuta have erect, terminal inflorescences (in addition to accessory axillary inflorescences) with orange/golden trichomes, whereas C. macrocarpa has long, pendant, ramiflorous inflorescence with white/grey trichomes. The petiole of C. hirsuta also differs in generally not exceeding 1 cm long, whereas C. sarmentosa and C. macrocarpa have a petiole that measures 1–2 cm long. The subglobose to ellipsoid ovary with its very short style distinguishes C. macrocarpa from C. hirsuta and C. sarmentosa , which have an ovary and style forming a slender structure whose parts are difficult to distinguish. Two stigmas can be distinguished on the styles of C. hirsuta and C. macrocarpa , whereas there is only a single stigma in C. sarmentosa .

Conservation status:—The plant is only known from 2 subpopulations, both located within mining concessions ( Fig. 3 ) belonging to two different mining companies. Thus, the two subpopulations are considered as two distinct locations (sensu IUCN). The AOO calculated is 27 km ². In the case of the Bota Mere specimen, the area was the focus of a botanical inventory for possible future mining activities. Citronella hirsuta is assigned a preliminary conservation status of Endangered (EN B2 a,b(iii)) using the IUCN Red List criteria ( IUCN 2012).

Additional specimens examined (Paratypes):— New Caledonia, North Province, Col de Poro (Bota Mere), 21°22’00.42”S, 165°41’30.77”E, 10.II.2004 (fl.), Dagostini & Rigault 805 ( NOU015205 , NOU054724 ) ; Kouaoua , plateau, 25.VII.2005 (st.) [same individual as JM4045 ], Munzinger 2952 ( NOU008019 , P05250578 , P05250579 ) ; Route de Poro , 21°22’24.31”S, 165°44’9.17”E, 6.IV.2007 (young fr.), Munzinger & Chapelle 4364 ( NOU017767 ) .

Figures

FIGURE 1. Comparison of trichomes on the inflorescence axes of the three species of Citronella occurring in New Caledonia. A. Citronella hirsuta. B. Citronella sarmentosa. C. Citronella macrocarpa. (A. Munzinger et al. 4045. B. McPherson 5470. C. MacKee 12894).

FIGURE 2. Citronella hirsuta. A. Habit. B. Leaves and inflorescence. C. Hirsute leaf. D. Scorpioid cyme. E. Part of an inflorescence with an open flower. F. Sepal. G. Petal. H. Stamen. I. Gynoecium. J. Fruit. Drawn by Laurence Ramon from Dagostini & Rigault 805, Munzinger & Chapelle 4364, field pictures by JM (for A & B).

FIGURE 3. Distribution of Citronella hirsuta. Pale grey represents areas with ultramafic substrates, the black line shows the border between the North and South Provinces, and dark grey (inset) represents mining concessions (© SMC/DIMENC) in the area where the species occurs.