Sindora x changiensis L.M.Choo, Loo, W.F.Ang & K.Er, 2022

Choo, Le Min, Loo, Adrian Hock Beng, Ang, Wee Foong & Er, Kenneth Boon Hwee, 2022, A natural hybrid of Sindora (Fabaceae, Detarioideae) from Singapore, PhytoKeys 190, pp. 87-102 : 87

Sindora x changiensis L.M.Choo, Loo, W.F.Ang & K.Er nothosp. nov.

Figs 3 , 4 , 5

Sindora coriacea = Sindora coriacea (Baker) Prain × Sindora echinocalyx Prain.

Diagnosis.

Pod intermediate in character between the two parents, with a smooth surface like that of S. coriacea coupled with sparsely-set and fine spines which are much less dense than in S. echinocalyx . Flower calyx entirely smooth and without prickles, resembling S. coriacea . Ovary lacking the hairless patch in the centre, which is the case for S. coriacea . Instead, it is entirely pubescent with fine adpressed hairs, but without the minute protuberances or prickles that are seen in S. echinocalyx .

Type.

Singapore: Changi : 503 Cranwell Road, 1°23.335'N, 103°58.618'E, 6 May 2021, Choo et al., SING2021-265 (holotype SING, isotypes (BKF, K, KEP, L)) .

Tree up to 27 m tall, dbh up to 1.5 m, bole columnar, with slightly raised rings around the girth, not buttressed, bark grey to blackish, slightly cracked or flaky. Stipules early caducous, only present in young parts, semicircular, 1.2-1.4 cm long. Leaves compound, paripinnate, 3-4 jugate, rachis puberulous, 3.5-5.6 cm long; petiole 2-3 cm long; petiolules 4-5 mm long, puberulous, grooved, greenish brown when fresh but drying dark brown to black. Leaflets opposite, coriaceous, elliptic, slightly asymmetric with midrib slightly curved, 3.5-6.8 × 2.3-3.5 cm, increasing in size up the rachis, base rounded to obtuse, apex acuminate to obtuse, with a very slight emarginate indent at the very tip; upper surface slightly glossy when fresh, but reticulations become conspicuous when dry, entirely glabrous, midrib flat to slightly sunken; lower surface glaucous, puberulous with tiny short golden hairs, midrib raised and also puberulous; thickened marginal vein either glabrous or minutely puberulous; reticulations clear and raised on both the upper and lower surfaces; one gland present on the tip of the midrib on the lower surface, another present on the thickened marginal vein close to the base of the leaflet. Inflorescence paniculate, both terminal and axillary, but mostly concentrated on the crown, growing from old stems where inflorescence branches from the previous year have been shed, flowering rachises long and stout, measuring 11.5-25 × 5-8 cm, side branches straight but bearing scars where the flowers are attached, branches flexible but held erect in fresh specimens. Both flowering rachis and branches completely pubescent with short golden adpressed to upright hairs. Bracts not seen, caducous; bracteoles ovate, c. 2.5 × 1.3 mm, pubescent on both surfaces, caducous, only seen in inflorescences where the buds are still small and developing. Pedicels 4.5-6 mm long, pubescent, receptacle short, 1-1.5 mm long; buds obovoid to ellipsoid, suture lines of the sepals becoming evident as the bud matures, measuring 6-7.5 × 4.5-5.5 mm when mature just before anthesis. Flowers strongly zygomorphic. Sepals 4, unequal, lanceolate to elliptic, 8.0-9.3 × 3.0- 5.2 mm, outer surface pubescent with small golden hairs, unarmed, inner surface densely covered with long golden brown tightly adpressed hairs. Petal 1, not exserted but nestled within the largest sepal during anthesis, rolled up and containing a drop of sweet floral-scented nectar, c. 7.5 × 2.2 mm when rolled up, top of petal with a well-defined hood fringed with long villous hairs which narrows off with the lower half of the petal with inrolled sides forming a closed tube; outer surface glabrous at the top and down the middle, densely pubescent at the sides and the lower half of the petal; inner surface glabrous; margins villous, colour pink tinged with green at the tip. Stamens 10, diadelphous, united basal portion of the stamens 2.5-3 mm long; two largest filaments 12-15 mm long, the seven in the middle of the bundle 6-7 mm long; two largest anthers elliptic, 2.5-2.7 × 1.7-1.9 mm, the others smaller and heart shaped, 1.6-2 × 1-1.4 mm, all nine mentioned here with visible pollen; final stamen on the other side of the flower is a staminode, 6-7.5 mm long but without a fertile anther. Ovary rhomboidal, densely covered all over with long silky villous hairs, except in three strips on the surface where the hairs are less dense; 3.5-4.5 × 2.8-3 mm, stipe 1.8-2.2 mm long, style glabrous except for the base where it has villous hairs like the rest of the ovary, 12-13.5 mm long, pale yellow green tinged with pink at the base, stigma capitate with small sticky papillate protuberances, c. 0.6 mm diameter. Pod a flattened, elliptic, rhomboidal or ovate two-valved dehiscent pod, surface sparsely armed with c. 20 or fewer slender spines that sometimes exude a clear resin; surface beneath the spines smooth and puberulous with short golden hairs, 7-8 × 6-6.5 cm, stipe 8-9 mm, beak 9-10 mm. Seed 1, aril trapezoid, yellowish brown to chestnut brown, 2.2-2.6 × 1.5-1.7 × 0.8-11 cm; seed 2-2.5 × 1.7-1.9 × 0.8-0.9 cm, surface smooth with fine horizontal cracks, black in colour.

Distribution.

The hybrid is likely endemic to Singapore. It is only known to occur naturally in Changi, which is at the north-east coast of Singapore, although the offspring of the tree has been propagated and planted elsewhere in Singapore as roadside trees.

Etymology.

Latin, - ensis = from, meaning "from Changi".

Habitat and ecology.

The species is part of the remnant vegetation of tropical lowland forest that was once present in the area, before it was cleared.

Phenology.

Flowers from April to May, and fruits in August.

Conservation.

Only a single tree of S. x changiensis is known to occur from the wild in Singapore, although the offspring of this tree have been planted elsewhere in Singapore as roadside trees.

Taxonomic notes.

In Sindora , the leaves of seedlings, saplings and water shoots of mature trees often have a morphology different from that of the mature leaves from the crown of the tree. The leaves of Sindora seedlings, saplings and water shoots are usually larger in size and are pubescent on the underside and along the leaflet margins, and the shape of the leaf and the leaf apex may differ somewhat from the mature leaves ( de Wit 1949; Choo and Ngo 2020). For the identification of this hybrid, pod characters are the most diagnostic, followed by flower characters, although fallen mature leaflets picked from below the tree may be useful in supplementing the fruit and flower characters.

Figures

Figure 3. The hybrid tree Sindora x changiensis A overview of the 27 m tall tree B developing (green) and ripe (brown) pods on the tree C inflorescences of the tree. (Photos: A K. B. H. Er, B, C L. M. Choo).

Figure 4. Comparisons of leaf and flower characters between Sindora x changiensis and its parent species. A, B, C leaves of (A) S. coriacea, (B) S. x changiensis and (C) S. echinocalyx respectively D, E, F flowers of (D) S. coriacea, (E) S. x changiensis and (F) S. echinocalyx respectively, showing the unarmed calyces of S. coriacea, S. Sindora x changiensis, and the spiny calyx of S. echinocalyx G, H, I Ovaries of (G) S. coriacea, (H) S. x changiensis and (I) S. echinocalyx respectively, showing the glabrous patch in the centre for S. coriacea; the densely pubescent ovary for S. x changiensis except for the three stripes across the width; and the densely pubescent ovary for S. echinocalyx, with tiny protuberances visible on the surface, which will later on develop into the spines on the fruit pods. Scale bars: 1 cm (A, B, C); 1 mm (D, E, F, G, H, I). (Photos: L. M. Choo).

Figure 5. Comparisons of pod and seed characters between Sindora x changiensis and its parent species A, B, C pods of (A) S. coriacea, (B) S. x changiensis and (C) S. echinocalyx respectively, showing the unarmed pod of S. coriacea, the sparsely spiny pod of Sindora x changiensis, and the densely spiny pod of S. echinocalyx D, E, F seeds of (D) S. coriacea, (E) S. x changiensis and (F) S. echinocalyx respectively. Scale bars: 1 cm (A, B, C, D, E, F). (Photos: L. M. Choo).