Ceriscoides glabra B.H.Quang, N.T.Cuong, T.D.Binh & Nuraliev, 2022

Binh, Tran Duc, Quang, Bui Hong, Cuong, Nguyen The, Quynh, Ha Quy, Hoan, Duong Thi, Hai, Do Van, Nguyen, Khang Sinh & Nuraliev, Maxim S., 2022, Ceriscoides glabra (Gardenieae: Rubiaceae), a new species from Kon Chu Rang Nature Reserve, southern Vietnam, Phytotaxa 574 (2), pp. 158-164 : 159-163

Ceriscoides glabra B.H.Quang, N.T.Cuong, T.D.Binh & Nuraliev , sp. nov. ( Figs. 1–3 )

Type: — VIETNAM. Gia Lai Province: K’Bang District, Son Lang Municipality, Kon Chu Rang Nature Reserve , primary broad-leaved forest, headwaters of Con river , right bank of Sai river above K50 waterfall ( Hang En waterfall), 14°31′12.3″N, 108°36′19.4″E, 866 m a.s.l., 25 July 2017, B. H. Quang, T. D. Binh, D. T. Hoan, D. V. Hai, K. S. Nguyen, D. H. Son KCR 46 [fl. & fr.] (holotype HN!; isotypes HN!, the herbarium of Kon Chu Rang Nature Reserve !) .

Additional specimen examined (paratype): — VIETNAM. The same location as in type, 06 September 2018, B. H. Quang, T. D. Binh KCR II 58 [fr.] ( HN!, mounted on 5 sheets) .

Etymology: —The specific epithet “glabra” refers to the remarkable entirely glabrous habit which distinguishes the new species from most of its congeners.

Diagnosis: —The new species differs from all the other species of Ceriscoides by the following combination of morphological characters: leaves glabrous, leaf blade mostly less than 6.5 cm long and less than 4 cm wide, with 3–4 pairs of secondary veins and without domatia, calyx (seen only in female flowers) glabrous with lobes more than 9 mm long, and corolla lobes (seen only in female flowers) more than 10 mm long and distinctly longer than wide.

Description:—Shrub or small tree, ca. 2 m tall, entirely glabrous (except for hair band within corolla tube). Branches terete, armed with paired thorns (modified short shoots produced in leaf axils of long shoots); thorns straight, stout, 1–3(3.5) cm long. Thorns commonly bearing tiny scale-like leaves and 1–2 lateral brachyblasts; brachyblasts with 2 (to several) foliage leaves and/or inflorescence. Brachyblasts (both vegetative and inflorescence-bearing) also produced in leaf axils of long shoots. Accessory shoots/buds rarely formed. Stipules interpetiolar, broadly triangular, ca. 3 mm long, with long attenuate (to nearly aristate) apex. Leaves opposite (decussate); petiole 1–6 mm long; blade dark green adaxially and pale green abaxially, chartaceous or subcoriaceous in sicco, ovate to elliptic or broadly lanceolate, (2)2.5–6.5(8.5) cm long, (0.8)1–3(4?) cm wide (leaves of brachyblasts somewhat smaller than those of long shoots), (1.8)2.0–2.7(3.2) times as long as wide, base narrowly to broadly cuneate (and sometimes decurrent), margins entire, apex acuminate; secondary veins 3–4 pairs, subopposite, domatia absent in vein axils abaxially, midvein and secondary veins more or less flat on both sides, tertiary veins inconspicuous. Inflorescence (with female flowers) apparently terminal on brachyblast (brachyblast borne on thorn or on long shoot), 1-flowered. Male flowers not seen. Female flowers actinomorphic, 5(6)-merous (except for gynoecium), ca. 3 cm long. Pedicel 2–3 mm long. Calyx light to dark green; tube narrowly campanulate, 2–4 mm long, ca. 2–3 mm in diameter at apex; lobes slightly unequal, elliptic to broadly elliptic or nearly rhomboid, ca. 10–15 mm long, 4–9 mm wide, 3-veined from base, base cuneate (lobes narrowly clawed), margin entire, apex acute. Corolla pale yellow; tube narrowly cylindrical-campanulate (gradually widening towards apex), ca. 15–18 mm long, ca. 3–4 mm in diameter at middle, inside with band of white hairs below middle; lobes widely spreading (rotate) to curved backwards, oblong to lanceolate, ca. 15 mm long, ca. 8 mm wide, margin entire, apex acute; petal aestivation contort, with lobes overlapping to the left in bud (also evident in anthetic flower). Stamens (apparently non-functional) inserted in distal part of corolla tube; anthers included in corolla tube, subsessile, dorsifixed, linear, ca. 5–6 mm long, 0.5 mm wide. Ovary inferior, light green outside, ovoid to ellipsoid, 10–12 mm long, 5–6 mm in diameter; style greenish white, columnar, gradually becoming thicker towards apex, ca. 17 mm long (together with stigma), surrounded at base with conspicuous yellow ring-shaped disk; stigma included in corolla tube (occupying level of anthers), green, fusiform, thicker than style, trigonal and apically shortly 3-lobed, ca. 5 mm long, ca. 2 mm in diameter. Fruit a berry (possibly, not fully mature fruits seen), pendant, fleshy, green, ellipsoid to ovoid, somewhat oblique, up to 8 cm long, up to 2.8 cm in diameter, crowned by persistent calyx, many-seeded; seeds lenticular, obliquely ovate in outline, 5–7 mm long, 3–4 mm wide.

Vernacular name (suggested here): —Găng nhẵn.

Phenology: —Flowering in July, fruiting from July to September.

Distribution: —The new species is currently known from a single location in Kon Chu Rang Nature Reserve, Vietnam.

Notes:—

1. Generic placement. Generic delimitation of the tribe Gardenieae is known to be highly complicated, and the taxonomic history of this tribe included numerous rearrangements ( Robbrecht & Puff 1986, Reza Azmi 2003, Mouly et al. 2014). Accordingly, identification of a specimen to the generic level is often far from being straightforward in this tribe. This is especially true for the thorn-bearing (“armed”) taxa, because species of similar habit are found not only in different genera of Gardenieae , but even in some other tribes of Rubiaceae ( Puff & Chamchumroon 2003) . We assign the species described here to Ceriscoides on the basis of several morphological peculiarities that rather unambiguously point to this genus: thorns bearing brachyblasts, 1-flowered female inflorescence, unequal calyx lobes, pale yellow corolla, and anthers and stigma included in corolla tube. Our identification is consistent with the generic keys provided by Puff & Chamchumroon (2003), Gardner et al. (2007, 2018) and Puff et al. (2021) for Thai Rubiaceae .

In addition, the new species apparently does not demonstrate secondary pollen presentation, similarly to all the currently known species of Ceriscoides and unlike numerous other genera of Gardenieae ( Puff et al. 1996; also, this character is coded as uncertain for Ceriscoides by Robbrecht & Puff 1986).

We describe the flowers of the new species as unisexual, which is a common character for Ceriscoides (although we have not evaluated the presence or absence of pollen in the anthers of the studied specimen). Interestingly, the unisexual flowers do not necessarily lead to the absence of the secondary pollen presentation in Rubiaceae , as a number of corresponding examples exist ( Puff et al. 1996).

2. Comparison with other species of Ceriscoides . Ceriscoides glabra is readily distinguishable from all its congeners by the following combination of morphological characters: leaves glabrous, leaf blade mostly less than 6.5 cm long and less than 4 cm wide, with 3–4 pairs of secondary veins and without domatia, calyx (seen only in female flowers) glabrous with lobes more than 9 mm long, and corolla lobes (seen only in female flowers) more than 10 mm long and distinctly longer than wide. Comparison of the floral features of C. glabra with those of the other species of Ceriscoides appeared problematic in some cases, because for some of the species only male flowers are known. However, in this genus, the floral indumentum, the colour of corolla and the shape of corolla lobes are similar in flowers of different sexual morphs within a species, and size of corolla does not differ more than twice (see Reza Azmi 2003). Therefore, certain rough discrimination is possible even if only the flowers of the opposite morphs are available for a species pair.

The new species is most similar to the Philippine endemic C. curranii ( Merrill 1918: 363) Tirvengadum (1983: 456) , which is especially evident from the key provided by Reza Azmi (2003). According to Reza Azmi (2003), C. curranii is very close to the widespread C. turgida , the only species hitherto known in Vietnam. Detailed morphological comparison among these three species is provided in Table 1 .

Figures

FIGURE 1. Ceriscoides glabra: habit and shoot system. A. Habit. B. Thorn bearing brachyblast; brachyblast bears leaves and young fruit. C. The same brachyblast-bearing thorn as in B, showing abaxial surface of leaf. Quang, Binh KCR II 58. Photos by H.Q. Bui, correction and design by M. Nuraliev.

FIGURE 2. Ceriscoides glabra: morphology of female flower. A. Branch with 1-flowered inflorescence. B. Flower (top view). C. Flower (side view). D. Flower (longitudinal section). Quang et al. KCR 46. Photos by H.Q. Bui, correction and design by M. Nuraliev.

FIGURE 3. Ceriscoides glabra: morphology of fruit and thorns; photos C–H taken from dried material. A. Fruit (side view). B. Fruit (longitudinal section). C. Thorn with lateral bud. D, E. Nodes of long shoots with axillary thorns. F. Fruit (cross section). G, H. Fruits (longitudinal sections; seeds removed in H). Quang et al. KCR 46 (A) and Quang, Binh KCR II 58 (B–H). Photos by H.Q. Bui, correction and design by M. Nuraliev.