Ziziphus ridleyana Rasingam & Karthig.

Cahen, D., Rickenback, J. & Utteridge, T.M.A. A revision of Ziziphus (Rhamnaceae) in Borneo. Kew Bull 76, 767–804 (2021). DOI: https://doi.org/10.1007/s12225-021-09970-3

Type

Malaysia, Sarawak, Lundu, s.d.Garai [Haviland’s collector] 881 (holotype: K [K000723014], isotype: K [K000723013]).

Morphology General Habit

Tree, small [height not measured but plant described as “small tree” on lectotype label], unarmed

Morphology General Crown

Crown, bole, bark, sapwood and heartwood features unknown

Morphology Branches

Branchlets terete, with longitudinal striations and visible lenticels, densely hairy on young parts and distal portions, more sparsely hairy when mature, hairs c. 0.3 mm long, mostly spreading, curved, reddish-brown

Morphology Leaves Stipules

Stipules not transformed into spines, early deciduous, narrowly triangular, c. 7 mm long, densely hairy

Morphology Leaves

Leaves weakly discolorous, drying greenish-brown, blade ± symmetric, elliptic-oblong, 14 – 31 × 3.5 – 11 cm, chartaceous to subcoriaceous, apex attenuate to acuminate, base obtuse to rounded, ± symmetric, margins subentire, obscurely serrate, each serration topped by a minute protruding callosity that dries darker than the lamina, c. 0.1 mm long; primary veins 3, impressed adaxially, raised abaxially, hairs dense along primary veins abaxially, hairs c. 1 mm long curved to tortuous, spreading to antrorse, reddish some whitish; strong marginal veins coming off the outside of the two outer main veins ˃ 30 on either side, all ending in a distinct intramarginal vein running along the leaf margin, angle of divergence with outer main veins c. 65°; transverse veins between the main veins conspicuous, also coming off midrib at c. 65°, raised (readily felt by touch), spaced by c. 5 (– 15) mm from each other; higher order reticulations visible; lamina hairy abaxially, hairs abundant; no domatia visible; petiole subterete, 5 – 15 mm long, hairs dense, indumentum extending to widened base of main veins adaxially

Morphology Reproductive morphology Inflorescences

Inflorescence of axillary short-peduncled, almost fascicle-like cymes, usually c. as long as subtending leaf’s petiole, 6 – 12 flowers in each cyme; pedicels to 4 mm, hairs dense; bracteoles entire, narrowly triangular, c. 5 mm long, hairy

Morphology Reproductive morphology Flowers

Flower hypanthium densely hairy on the outer surface; sepals triangular, c. 4 mm long, glabrous and keeled adaxially; petals clawed, c. 2 mm long, obcordate; stamen filaments flat, subulate, c. 2 mm long, anthers c. 0.4 mm long, exceeding petals; nectary disk pentagonal, rugose, appearing ± 20-pitted, glabrous, annulus strongly raised and sheathing style; style arms 3, c. 0.5 mm long, diverging, not expanding at apex, glabrous; ovary partially immersed

Morphology Reproductive morphology Fruits

Fruit unknown.

Distribution

Borneo (Sarawak), only known from vicinity of Mount Pueh.

Ecology

Borneo rain forest; alt. c. 600 m.

Conservation

Endangered (EN). Ziziphus ridleyana is only known from 2 collections in the Mount Pueh, Lundu area (the most recent from 1929) and Borneo rainforests have been declining in extent and quality. The species thus meets the B1ab(iii) criteria for EN status. Mount Pueh forests seem relatively well preserved on satellite imagery and Haviland’s collection may have been within GunongGading, an IUCN Category II (National Park) area.

Phenology

Collected in flower in Oct.