Senyumia minutiflora (Ridl.) Kiew, A. Weber & B.L. Burtt.

Short herb. Stem wiry, woody, to 20 cm long, 4–5 mm diameter, with a terminal rosette of many leaves. Indumentum pilose, of dense, long uniseriate hairs, intermingled with glandular hairs that make the lamina sticky to touch. Leaves opposite; petiole long, slender; lamina very thin, membranous, soft, pale green, broadly lanceolate to elliptic, 4–15 × 4–7.5 cm, margin toothed, teeth blunt, base not cordate, often unequal; veins 6–8 pairs. Inflorescences axillary, pair-flowered dichasial cymes, 9–17 cm long; pedicels very fine, 9–11 mm long. Flowers small; calyx divided to base into five narrowly lanceolate lobes, 1.5–2 mm long,; corolla white, sometimes tinged pink, tube very short, straight-sided, slightly dilating, 1.2–3 mm long, limb bilabiate, lobes in upper position densely studded with short glandular hairs internally, in non- or partially resupinate flowers, two lobes of the upper lip are strongly reflexed, in resupinate flowers, the lower three lobes held in the upper position are strongly reflexed; stamens 2, anthers large, 1.5–2 mm long, ellipsoid, cohering, yellow, exserted; nectary absent; ovary small, 2–3 mm long, ovoid; style 2–5 mm long, protruding; stigma punctiform. Capsules orthocarpic, 4–10 mm long, glabrous, strongly twisted, opening on the dorsal and ventral sides, valves becoming spiral after dehiscence. Seeds numerous, minute, 104–117 × 29–31 µm or 350 × 210 µm.

Two species, both endemic in Peninsular Malaysia.

Lithophytic, growing in cracks and crevices in light shade either on quartz derived from granite or on limestone rocks.

This new taxon resembles Senyumia minutiflora in its wiry, woody stem; tufted leaves with an elliptic lamina with a non-cordate base; small, white flowers and orthocarpic, strongly twisted capsule. However, the new species differs from Senyumia minutiflora in its shorter leaves that are less than 1.5 times longer than wide, flowers that are not resupinate or are partially resupinate, have a longer corolla tube and lobes of the lower lip that are flat and not reflexed and the much smaller seeds (Table 1).

Peninsular Malaysia. Johor, Ledang District, Bukit Tukau, 10 Dec 2009, Lau KH et al. FRI 68518 (holotype KEP!; iso.: K!, L!).

Perennial herb. Stem wiry, woody, ca. 4–12 cm tall, erect, 3.5–5 mm diameter. Indumentum densely woolly with long soft uniseriate, whitish hairs, dense on petiole, on lamina on upper surface and veins on lower surface, ca. 2 mm long interspersed with glandular hairs, lamina sticky to touch. Leaves opposite pairs spaced up to 6.5–8 cm apart; petiole fleshy, densely hairy, hairs 2–6 mm long, pale green, ca. 2 cm long in upper leaves, lengthening in lower leaves to 10.5 cm long; lamina broadly lanceolate to ovate, 4–6(–10) × (3–)7–7.5 cm, in life soft, light green above with long hairs ca. 2 mm long interspersed with glandular hairs, making the lamina sticky to touch, whitish-green beneath, base rounded, slightly to strongly unequal, apex acute, margin deeply crenate or serrate, teeth ca. 3 × 4 mm, to rounded to acute, tipped by a hair; lateral veins 6–8 pairs, deeply impressed above, prominent beneath and covered in long hairs ca. 2 mm long interspersed with glandular hairs, intercostal veins scalariform, ascending. Inflorescences 5–12(–17) cm long, with wispy long glandular hairs, a pair-flowered dichasium three times branched with 6–10 to many flowers; peduncle 3–9 cm, lateral branches short 1–2 cm long; pedicels erect, very fine, 8–13 mm long. Flowers not resupinate or partially resupinate; sepals pale green, divided almost to base, narrowly lanceolate, ca. 2 × 0.75 mm, densely glandular hairy, hairs ca. 0.5 mm long; corolla pure white, scintillating, sometimes tinged pink, ca. 7-13 mm long, outside with minute glandular hairs, tube short, not pouched, 2–3 × 2.5–4 mm, upper lip 2-lobed, 2–4 × 2.5 mm, erect, margin strongly reflexed, inner surface densely studded with short glandular hairs; lower lip glabrous, flat (not recurved) with 3 more-or-less isomorphic lobes, either lip more-or-less longer than broad, 5–9 × 6–7 mm with oblong lobes (Bukit Reban Kambing population, Fig. 1D, E) or broader than long, 4–7 × 6.5–8 mm and lobes rounded (Bukit Tukau population, Fig. 1B, C); stamens 2, filaments white, sinuous, 2–3 mm long; anthers large, pale yellow, 1.5–2 × 0.5 mm, cohering, protruding ca. 1.5 mm beyond the corolla tube; nectary absent; ovary pale green, glabrous, 2–3 × 1 mm; style white 2–5 mm, projecting beyond the corolla tube; stigma punctiform. Infructescence curling and positioned below the leaves. Capsules strongly twisted, 4–7.5(–10) mm long, ca. 1.5 mm diameter. Seeds numerous, minute, 80–117 × 29–31 µm.

Peninsular Malaysia, Johor, Ledang District, endemic on Bukit Reban Kambing and Bukit Tukau, on an isolated low range of granite hills from 200–500 m elevation, west of the southern tip of Gunung Ledang (formerly known as Mt Ophir).

From its habitat, it grows in cracks in quartz rocks derived from the granite bedrock, in contrast to Senyumia minutiflora that is restricted to growing on limestone rocks.

Critically Endangered B2a,biii. The total population probably amounts to less than 250 fertile individuals and is vulnerable because of its small and fragmented population. It is severely threatened by habitat disturbance and degradation. The forested ridge lies outside the network of Totally Protected Areas and is surrounded by oil palm plantations. The Bukit Tukau area has been logged and is currently the site of an active quarry. The area is being considered as an extension to the Gunung Ledang State Park to protect the Critically Endangered Cycas cantafolia.

In hill dipterocarp forest on ridges at 320–505 m elevation, below the tree canopy in light shade, on low cliff faces or vertical rocky outcrops of sedimentary rocks with quartzite inter-bedded with slate that has eroded to leave horizontal cracks where this species grows. It is a rare species known only from about four small populations, each with a few to about 60 fertile plants. From the many seedlings, it is apparently regenerating freely from seed. Plants with flowers and fruits were collected in July and December but in March and October only fruiting plants with abundant fruit were found. In March 2016 after a drought, its leaves were completely wilted and dried. It is not known if these plants can recover or whether the population will regenerate from seed. The woody stem shows that they are perennial plants.

There is some variation between populations. The populations on Bukit Reban Kambing have flowers that are never resupinate, are pure white and are slightly larger, the lower lip measuring 5–9 × 6–7 mm (Fig. 1D, E) compared with flowers from the Bukit Tukau population that, in some flowers, are partially resupinate (Fig. 1B), the lower lip is proportionally broader, measuring 4–7 × 6.5–8 mm and, in some individuals, the corolla is tinged pale pink (Fig. 1C). Otherwise, they are the same in calyx, corolla tube, stamen and carpel characters. It is tempting to suggest that these two forms should be given taxonomic recognition. However, very few flowers from the Bukit Tukau population were available to study variation in this population. Indeed, further investigation of the two populations may result in the recognition of two separate taxa, perhaps at an infraspecific rank.

Peninsular Malaysia. Johor: Ledang District, Bukit Tukau (2°20.04'N, 102°32.3'E), 30 Oct 2009, Lau et al. FRI 68516 (KEP!, SING!); ibidem, 27 July 2010, Lau et al. FRI 68524 (KEP!); Ledang District, Bukit Reban Kambing (2°20.04'N 102°32.46'E), 8 March 2016, Fakrul et al. FRI 85653 (KEP!); ibidem, 10 March 2016, Fakrul et al. FRI 85672 (KEP!).

Figure 2. 

Distribution of Senyumia granitica (●) and S. minutiflora (▲).