Similar to Codonoboea rheophytica Kiew in its rheophytic habit, distinct narrow leaves, serrate leaf margin and numerous lateral veins but it differs in its cymose inflorescence with 2–3 flowers (C. rheophytica has one-flowered inflorescences), small tubular flowers (1–1.3 cm vs. 3–3.5 cm long) and flower colour, violet not white as in C. rheophytica.

Figure 1. 

Illustration of Codonoboea kenaboiensis Syahida-Emiza, Y.Y.Sam & Siti-Munirah, sp. nov. A habit B leaf section show midrib and reticulate vein C inflorescence D flower opened to show position of stamens E calyx with pistil F nectary annular G stigma H stamens I fruit (All from FRI 87630, drawn by Mohamad Aidil Noordin).

Peninsular Malaysia. Negeri Sembilan: Jelebu, Kenaboi Forest Reserve, 3°10'N, 101°59'E, 11 July 2019, Syahida Emiza, S., Sam, Y.Y. & Angan, A. FRI 87630 (holotype: KEP; isotype: K, SING).

Figure 2. 

Codonoboea kenaboiensis Syahida-Emiza, Y.Y.Sam & Siti-Munirah, sp. nov. A, B habitat C, D habit E fruits F flowers G corolla lobes (front view).

Rheophyte, 10–20 cm tall. Stems woody, erect, wiry, unbranched. Leaves decussate, pairs spaced up to 0.5 cm apart, denser to the apex; petioles slender, 0.5–1 cm long, c. 0.1 cm diameter; laminas narrowly elliptic, 4.5–10 × 0.8–1 cm, coriaceous, mid-green above, pale green beneath, base attenuate, apex acute to attenuate, margin serrate; midrib and lateral veins sunken above, glabrous, prominent beneath, puberulous, lateral veins up to 30 pairs, generally opposite or alternately arranged, intercostal veins reticulate, slightly prominent. Inflorescences at upper leaf axils, erect, 1 per axil, cymes, 2–3-flowered; indumentum of floral parts a combination of glandular and simple hairs; peduncle 4–8 cm, purplish-maroon, densely hairy; bracts 3–3.5 × c. 1 mm, densely hairy, lanceolate, apex blunt. Flowers: pedicels 2–3 mm long, purplish, densely hairy; calyx mid-green, densely hairy, 5-lobed, narrowly lanceolate, lobes 1.2–1.5 × 0.2–0.8 mm, apex blunt; corolla tubular, 10–13 mm long, base 2 mm wide, dilating to 3 mm at the mouth, outside whitish to violet, sparsely hairy, inside whitish, glabrous, veins conspicuous; corolla lobes deeper violet, unequal in size, oblong, c. 3 × 2 mm, apex blunt; stamens 2, 3–3.5 mm long, filaments erect, c. 2.5 mm long, glabrous, anthers versatile, c. 0.8 mm long, c. 1 mm wide, white; nectary annular, c. 0.6 mm tall, rim toothed, glabrous; pistil yellowish-cream, c. 8 mm long, ovary c. 3.5 × 0.7 mm, sparsely hairy, style c. 4.5 mm long, white, sparsely hairy, stigma peltate, c. 0.7 mm across, papillose. Capsules cylindrical, 18–20 mm long, c. 1 mm wide at base, green, splitting adaxially when mature, calyx persistent. Seeds elliptic-oblong, c. 0.2 × 0.15 mm.

Peninsular Malaysia. Negeri Sembilan: Jelebu, Kenaboi Forest Reserve, 6 May 2010, Mohd. Hairul, M.A. et al. FRI 70988 (KEP).

Endemic in Negeri Sembilan, Peninsular Malaysia. Currently known only from the type locality.

Map 1. 

Distribution of Codonoboea kenaboiensis (circle) and Codonoboea ruthiae (triangle) in Peninsular Malaysia.

Lowland dipterocarp forest, on rocks or steep earthy river banks, at 275–315 m altitude. Flowering from May to July. Codonoboea kenaboiensis grows on the lower levels of the riparian zone to about 1.5 m above the normal water level. Conditions are cool and damp with a thick layer of mosses covering the ground and shrubs and trees on higher ground leaning towards the river providing partial shade to the vegetation underneath. Such conditions are ideal for many plants but they are subjected to regular flooding events such as flash floods and annual floods during monsoon seasons. Only plants with rheophytic adaptations like C. kenaboiensis can survive the swift moving flood water. It has narrow leaves and roots that secure it firmly to the ground, preventing it from being uprooted by water currents. However, more frequent and intense flooding as a result of climate change might affect its long-term survival at Sungai Kenaboi.

The epithet refers to the Kenaboi State Park, its only known locality.

Vulnerable, VU D2. Codonoboea kenaboiensis is hyper- endemic with a very small and restricted population at Sungai Kenaboi, Kenaboi State Park. Its small population and position in the flood zone is threatened by the increasing records of flood and extreme weather events caused by climate change. Tang (2019) has projected more rainfall events of high intensity and tropical storms in Malaysia as climate change intensifies. Under such circumstances, the seeds and seedlings of C. kenaboiensis will be washed away before they can firmly establish to the substrate thereby affecting its regeneration. Following the IUCN Standards and Petitions Committee (2019), C. kenaboiensis qualifies for VU D2 because the increased frequency of floods is expected to cause a population reduction and, due to its small population, the species could become Critically Endangered or Extinct in a very short period of time.

Codonoboea kenaboiensis belongs to Codonoboea sect. Pectinati, characterised by narrow and serrate to deeply toothed leaves and small tubular flower (Ridley 1923; Lim and Kiew 2014). It closely resembles C. rheophytica, a recently described rheophyte from Terengganu (Kiew and Lim 2019). Both have distinctly narrow leaves (0.8–1 cm in C. kenaboiensis and 0.8–1.3 cm in C. rheophytica), serrate leaf margins and numerous lateral veins (30 pairs in C. kenaboiensis and 33–36 pairs in C. rheophytica). However, they are distinguished by the inflorescence and floral structures. Codonoboea kenaboiensis has simple cymes bearing 2–3 tubular flowers whereas C. rheophytica has solitary trumpet-shaped flowers. In addition, the violet flowers of C. kenaboiensis are much smaller (c. 1–1.3 cm vs 3–3.5 cm in C. rheophytica) than the white flowers of C. rheophytica.

Codonoboea species are common on stream and river banks but very few are true rheophytes. Other than C. rheophytica and C. kenaboiensis, C. densifolia (Ridl.) C.L.Lim and C. salicina (Ridl.) C.L.Lim are two other rheophytes found in Peninsular Malaysia (Kiew 1987). The narrow leaves of C. densifolia and C. salicina have entire to serrulate margins and fewer lateral veins (up to 20 pairs) that clearly distinguish them from C. kenaboiensis. In terms of inflorescence structure, both C. densifolia and C. salicina have cymose inflorescences similar to C. kenaboiensis but their campanulate flowers are distinct from the tubular flowers of C. kenaboiensis.

At Sungai Kenaboi, there is another Codonoboea species growing on the steep riverbanks. Codonoboea breviflora can easily be mistaken as a larger form of C. kenaboiensis that also has long narrow leaves and serrate leaf margin. However, the leaves of C. kenaboiensis are conspicuously smaller with shorter petioles (0.5–1 cm vs 1–2.5 cm long) and smaller laminas (4.5–10 × 0.8–1 cm vs 9–20 × 2.5–5.5 cm) compared to C. breviflora (Fig. 3). Upon closer examination, the leaf venation of C. kenaboiensis also proves to be distinct from C. breviflora. Codonoboea kenaboiensis has craspedodromus lateral veins (the veins run directly from midrib to the margin) whereas in C. breviflora the veins branch before reaching the margin. In addition, the single campanulate flower of C. breviflora instantly differentiates it from C. kenaboiensis.

Figure 3. 

A, B Codonoboea rheophytica C, D Codonoboea densifolia E, F Codonoboea salicina G, H Codonoboea breviflora I ck = Codonoboea kenaboiensis, cb = Codonoboea breviflora.

Both C. kenaboiensis and C. breviflora grow at Sungai Kenaboi, but based on observations they occupy different sections of the flood zone. Codonoboea kenaboiensis resides on the lower levels of the river banks that are less than 1.5 m above the normal water level whereas C. breviflora is found at slightly higher levels more than 2 m above the water level. The higher ground is less affected by floods and supports a denser vegetation compare to the site of C. kenaboiensis.

Amongst species in Codonoboea sect. Didymanthus, Codonoboea ruthiae is most similar to C. ramosa (Ridl.) Kiew, but can be distinguished by having a larger lamina (9.5–15.5 × 3.5–6.2 cm vs 5.1–7.6 × c. 3.8 cm) with more lateral veins (10–12 vs c. 7 pairs); the inflorescences in C. ruthiae consists of 5–6 flowers (only 2 in C. ramosa) with larger flowers (corolla tube 1.7–1.9 cm long vs c. 1.3 cm long) and flower colour (maroon vs greenish yellow)

Figure 4. 

Illustration of Codonoboea ruthiae Syahida-Emiza, Y.Y.Sam & Siti-Munirah, sp. nov. A habit B inflorescence C calyx D flower opened to show position of stamens E pistil F anthers G stigma H bract I fruit (All from FRI 86960, drawn by Mohamad Aidil Noordin).

Peninsular Malaysia. Negeri Sembilan: Jelebu, Kenaboi Forest Reserve, 3°10'48.6"N, 101°58'19.9"E, 30 October 2017, Syahida Emiza, S., Sam, Y.Y., Yap, J.W., Angan, A. & Markandan, M. FRI 86960 (holotype: KEP)

Figure 5. 

Codonoboea ruthiae Syahida-Emiza, Y.Y. Sam & Siti-Munirah. A habitat B habit C inflorescence with flower and pistil (corolla fallen) D flowers from front view E flower and fruits F longitudinal section of flower G capsule.

Erect, perennial herb, 20–50 cm tall. Stems slender-branched, 3–4 mm diameter, semi-woody at base. Leaves decussate, pairs spaced up to 4.5 cm apart, very unequal; petioles slender, grooved above, pale green, puberulous to glabrescent; smaller leaves less than half the size of larger leaves, petioles 0.5–1.5 cm, c. 0.1 cm diameter, laminas 5.5–7.5 × 1.5–3 cm; larger leaf with petioles 1.0–3.2 cm long, c. 0.1 cm diameter, laminas lanceolate to ovate, 9.5–15.5 × 3.5–6.2 cm, asymmetric, thinly coriaceous, mid-green above, glabrous, pale green beneath, sparsely puberulous to glabrescent, base oblique, apex acute, margin serrulate, sparsely puberulous; midrib and lateral veins raised on both surfaces, sparsely puberulous to glabrescent, lateral veins 10–12 pairs, alternately arranged, intercostal veins reticulate, slightly prominent. Inflorescences at upper most leaf axils, erect, pair-flowered cyme twice branched with 5–6 flowers; indumentum of floral parts a combination of glandular and simple hairs, simple hairs 0.75–1 mm long; peduncle 4–5 cm, reddish green, densely hairy; bracts and bracteoles lanceolate, bracts c. 3.2 × 0.7 mm, bracteoles c. 2.5 × 0.5 mm. Flowers: pedicels 2–10 mm long, greenish maroon, densely hairy; calyx mid-green, densely hairy, 5-lobed, calyx lobes three quarters of the calyx length, lobes narrowly acute, 2.1–2.5 × 0.4–0.5 mm, apex slightly blunt; corolla trumpet-shaped, 20–24 mm long, base narrow, 1–1.5 mm wide, dilating to 7–8 mm wide at mouth, tube 17–19 mm long, veins conspicuous, outside pale maroon, sparsely hairy and hirsute, inside with deep maroon streaks, throat with two yellow nectar guides, veins conspicuous, pubescent from base up to stamens attach, upper lobes nearly rounded, c. 4 × 5 mm, slightly reflexed, side lobes rounded c. 5 × 5 mm, lower lobe near transverse elliptic, c. 5 × 7 mm; stamens 2; filaments slender, c. 5.3 mm long, glabrous, slightly curved upward, attached to corolla tube at c. 7 mm from base, anthers reniform, small, c. 2 mm long, 0.6 mm wide, white, dorsifixed, fused face-to-face; nectary annular, c. 1.3 mm tall, rim undulate, glabrous; pistil whitish-cream, c. 13 mm long, ovary 7–8 × c. 0.6 mm, glabrous; style 5–6 mm long, white, sparsely hirsute; stigma peltate, c. 0.8 mm across, papillose. Capsules cylindrical, very slender, 25–40 mm long, 1–1.5 mm wide, maroon-green, densely hairy, splitting adaxially when mature; calyx persistent. Seeds elliptic-oblong, c. 0.3 mm × 0.25 mm.

Peninsular Malaysia. Selangor: Hulu Langat, Sungai Lalang Forest Reserve, Compartment 42, 29 June 2004, Sam Y.Y. et al. FRI 47248 (KEP), Compartment 43, 13 February 2019, Sam Y.Y. et al. FRI 69261 (KEP, K, L, SAN, SAR, SING).

Peninsular Malaysia, recorded in Negeri Sembilan and Selangor.

In lowland dipterocarp forest, on forest floor, hill side or slope near shaded small stream at 130–335 m altitude. Flowering in February, June and October.

Named after Dr. Ruth Kiew, a prominent botanist, plant taxonomist and conservationist. She is well known for her work on herbaceous plants such as begonias and gesneriads, and also limestone and montane flora.

Least Concern (LC). Codonoboea ruthiae is well protected within the Protected Area Network. Its existence in Kenaboi State Park and also at the water catchment forest in Sungai Lalang Forest Reserve, Selangor, which is categorised as a Protection Forest, is legally secured under the National Forestry Act 1984 (Ministry of Water, Land and Natural Resources 2019). Furthermore, no threat to the species population has been identified.

Codonoboea ruthiae belongs to Codonoboea sect. Didymanthus (Lim and Kiew 2014) characterised by opposite and well-spaced petiolate leaves. It closely resembles C. ramosa in its slender-branched stem, distant pairs of leaves, one of each pair much smaller, oblique lamina base and trumpet-shaped flowers (Ridley 1923). However, C. ruthiae can be distinguished from C. ramosa by a combination of characters shown in Table 1.