Mezoneuron kauaiense (H. Mann) Hillebrand, 1888

Clark, Ruth P., 2016, A Taxonomic Revision of Mezoneuron (Leguminosae: Caesalpinioideae: Caesalpinieae), Phytotaxa 274 (1), pp. 448-450 : 448-450

14. Mezoneuron kauaiense (H. Mann) Hillebrand

Flora of the Hawaiian Islands. W.F. Hillebrand, London, Williams & Norgate: 110–111. 1888.

Type:— HAWAII, Kauai, Waimea , Kaawaloa , Mann, H. & Brigham, W.T. s.n. Holotype CU; isotype BISH (BISH1009127, image!).

Basionym. Caesalpinia kavaiensis H. Mann. Proc. Amer. Acad. Arts vii: 164. 1867.

Tree to ca. 12 m high. Stems unarmed; sparsely to densely whitish to orange tomentose. Stipules caducous; triangular; ca. 1–2 × 1 mm, partially tomentose. Leaves with 2–4 pairs pinnae; 4–5 [–8] pairs leaflets per pinna; petioles 2–9.5 cm; leaf rhachis 5–22 cm, unarmed; pinnae opposite or subopposite, 3.5–11 cm, the basal pair shorter than the others; leaf rhachis, petiole, and pinna rhachis sparsely to densely orange tomentose or villous, petiolules sometimes more densely hairy than rhachis. Leaflets opposite to alternate; the terminal leaflets elliptic to oblong, base strongly oblique, apex retuse to emarginate; 2–5 × 1–2 cm; lateral leaflets elliptic to oblong, base strongly oblique, apex retuse to emarginate; 1.5–4.5 × 0.9–1.9 cm; all leaflets with upper surface glabrous, lower surface with a dense tuft of villous hairs at the base, the hairs extending part way or all the way along the midvein, otherwise glabrous; 2˚ venation anastomosing, 3˚ venation reticulate, veins slightly visible above, clearly visible below. Inflorescence a raceme to ca. 50 cm, usually terminal, occasionally axillary or arising from the stem independently from the leaves; the axes glabrous, or subglabrous, with hairs only at base of pedicels, or sparsely to moderately orange tomentose; pedicels 23–50 mm, articulated 5–10 (– 15 in fruit) mm below hypanthium, glabrous, or occasionally with few hairs at articulation. Bracts not seen, apparently absent; bracteoles caducous, triangular, the apex acuminate, ca. 4–5 × 2 mm; densely pale orange tomentose at base and sides, glabrescent towards apex. Flowers with a hypanthium 8–11 × 3–4 mm; lower calyx lobe 13–14 × 6–7 mm; other lobes 9–11 × 5–7 mm; hypanthium and calyx lobes glabrous; veins clearly visible in calyx lobes. Median petal broadly obovate, tapering to a broad claw, strongly laterally inrolled, 8–10 × 7–12 mm, blade ca. 4–5 × 8–12 mm, claw ca. 1–5 × 1–4 mm, glabrous or with few hairs on claw. Upper lateral petals elliptic to suborbicular, ca. 10–12 × 8–12 mm, including

26 • Phytotaxa 274 (1) © 2016 Magnolia Press

CLARK

A TAXONOMIC REVISION OF MEZONEURON

Phytotaxa 274 (1) © 2016 Magnolia Press • 27 claw ca. 1 mm long, glabrous. Lower laterals petals elliptic, tapering to a claw, ca. 12–14 × 6–9 mm, including claw ca. 2–3 mm long, glabrous; veins prominent on all petals. Stamen filaments flattened, 10–22 mm long, with translucent orange hairs on the basal ½, on both surfaces, or sometimes on margins only; anthers ca. 2 mm long. Ovary glabrous, ca. 6–9 mm long, style ca. 12–20 mm long; style tapering to a narrowly cupular stigma, this very slightly papillate. Fruit ligneous, usually glaucous with white waxy coating; broadly elliptic to oblong, base obliquely attenuate to cuneate, apex retuse, or the wing extending to form a beak; 6.5–12 × 4–6 cm, wing 5–12 mm wide; glabrous; venation reticulate, faintly visible or slightly raised on fruit body, not visible on the wing; hypanthium persistent. Seeds 2–4; pale brown, transversely arranged, ovoid, flattened, 1.8–2 cm long, 1.4–1.6 cm wide; not visible individually in outline on fruit exterior. ( Fig. 15 ).

Distribution:—Endemic to Hawaii, islands of Hawaii, O’ahu and Kaua’i. ( Fig. 16 ).

Habitat and ecology:—Dry hills; dry and moist forest; degraded native vegetation, mostly Aleurites lowland mesic forest. Elevation 80–920 m.

Phenology:—Flowering and fruiting throughout the year.

Conservation Assessment:—Critically Endangered (CR) ver. 3.1 ( IUCN 2015). Mezoneuron kauaiense is endemic to the islands of Hawaii and Oahu. Eight subpopulations are known, totalling 60 individuals, however, many of these are senescent and probably non-reproductive. Threats include pigs, cattle, deer, goats, introduced plants, rats, fire, volcanic eruptions, sheep, black twig borer and collection by humans ( IUCN 2015).

Field notes:—Petals red.

Figures

FIGURE 15. Illustration of M. kauaiense (drawn by Eleanor Catherine).

FIGURE 16. Distribution of M. kauaiense in Hawaii.