Xanthophytum antoanense Luu, H. C. Nguyen, X. B. Nguyen-Le & Q. D. Nguyen, sp. nov.
Creators: name: Nguyen, Hieu Cuong
name: Nguyen-Le, Xuan Bach
name: Nguyen, Quoc Dat
name: Nguyen, Tran Quoc Trung
name: Luu, Hong Truong
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Plantae
Tracheophyta
Magnoliopsida
Gentianales
Rubiaceae
Xanthophytum
Xanthophytum antoanense

description: Xanthophytum antoanense Luu, H. C. Nguyen, X. B. Nguyen-Le & Q. D. Nguyen sp. nov.
Fig. 1
Type.
Vietnam • Binh Dinh Province, An Lao District, An Toan Commune, An Toan Nature Reserve, coordinates 14°31'31"N, 108°42'48"E, 838 m elevation, 17 May 2023, Nguyen Le Xuan Bach, Nguyen Quoc Dat, Nguyen Hieu Cuong BN 1015 (Holotype: SGN!, barcode SGN 006396).
Diagnosis.
The new species is morphologically closest to X. capitatum Valeton but differs from the latter by its 3 - lobed (vs. unlobed) stipules, narrowly lanceolate (vs. oblong to obovate) leaf blades with a cuneate-oblique (vs. symmetrically cuneate to attenuate) base and 20–22 (vs. 11–16) pairs of secondary veins, 3.5–4.5 (vs. 0.5–3) cm long peduncle, spatulate (vs. bluntly triangular) calyx lobes, larger flowers with a 5–5.4 (vs. c. 1.8) mm long corolla tube and 2.4–3 (vs. c. 0.7) mm long corolla lobes, and an apically hairy (vs. glabrous) style.
Description.
Monocaul dwarf shrublet, sub-herbaceous, to 50 cm tall. Stems densely hairy, hairs septate, red, c. 1 mm long. Leaves simple, opposite, decussate; petiole 4–6 cm long, c. 0.35 cm in diameter, densely hairy with hairs septate, red, c. 1.5 mm long; lamina elongate-lanceolate, 13–24 cm long, 3–4.5 cm wide, adaxially green, glabrous, abaxially gray, densely hairy, hairs setose, red, c. 1.5 mm long; base cuneate-oblique, apex acute; venation pinnate, midrib prominent on both surfaces, adaxially sparsely and abaxially densely hairy, hairs c. 1.5 mm long, secondary veins 20–22 pairs, weakly brochidodromous, tertiary veins abaxially prominent. Stipules 1.7–2.5 cm long, 1.2 cm at widest, ovate, acuminate, slightly 3 - lobed, abaxially densely hairy, hairs septate, red, c. 1.5 mm long. Inflorescences axillary, pseudo-terminal heads, erect then nodding, heads c. 2 cm in diameter, many-flowered; peduncles 3.5–4.5 cm long, 0.2–0.3 cm in diameter, densely hairy, hairs septate, red, c. 1.3 mm long. Bracts oblanceolate, 3.0– 3.2 mm long, 1.1–1.3 mm wide, white, apically red-violet, ciliate, abaxially densely hairy, hairs septate, red, c. 1 mm long. Interfloral bracts linear, c. 3.5 mm long, 0.25 mm wide, white, abaxially densely hairy, hairs septate, red, c. 0.6–0.8 mm long. Flowers bisexual, probably heterostylous, sessile, c. 1.1 cm long. Calyx 5 - lobed, lobes spatulate, white, apically red, 7–8 mm long, c. 1.6 mm at widest, adaxially glabrous, abaxially densely hairy, hairs septate, red, c. 1 mm long. Corolla white, turning brown, tubiform with spreading lobes; tube 5–5.4 mm long, 1.2–1.4 mm in diameter, outside glabrous, inside densely white tomentose on upper ¾, hairs 0.4–0.5 mm long; lobes 5, 2.4–3 mm long, 0.7–1 mm at widest, oblong-lanceolate, acute, outside white to red setose with 0.5–0.6 mm long stiff hairs, inside papillose. Stamens 5, inserted at corolla base, 5.3–5.5 mm long; filaments c. 5 mm long, glabrous; anthers c. 1 mm long, dorsifixed, longitudinally dehiscent. Pistil 4.8–5.0 mm long; disc white, hemispherical, c. 0.5 mm high; ovary 2 - celled, c. 2 mm high, 1.5 mm wide, densely red septate hairy; ovules numerous on a globose, axile placenta in each cell; style 2.7–2.8 mm long, gradually thickened towards the apex, sparsely hairy on upper half; stigma 2 - lobed, lobes lanceolate, with obtuse apex, c. 1.3–1.4 mm long. Fruit unknown.
Etymology.
The species epithet is derived from the location where the new taxon was discovered.
Vernacular name.
Hoàng cành An Toàn (Vietnamese).
Phenology.
Flowering observed in May; fruiting is unknown.
Distribution and ecology.
The species is known only from An Toan Nature Reserve (Binh Dinh Province, Vietnam). It grows on moist fertile soils in lower montane evergreen forests at elevations around 850 m. The forest is dominated by Rubiaceae, Fagaceae, Lauraceae, Myrtaceae, Clusiaceae, and Fabaceae.
Preliminary IUCN conservation status.
Data Deficient (IUCN Standards and Petitions Subcommittee 2024). The new species appears to be rare and was discovered in a small population. Its actual distribution and population size cannot be assessed at present, but the species is likely to occur in adjacent forests in Gia Lai and Quang Ngai Provinces. Further surveys are necessary to determine its precise conservation status.
Taxonomic notes.
Axelius (1990) identified ferruginous indumentum as a synapomorphy for Xanthophytum species. Despite variations in color and density among species, the indumentum generally consists of two kinds of hairs: multicellular (septate) and unicellular. Septate hairs are found on vegetative parts and the exterior of the calyx and corolla, while unicellular hairs are located inside the corolla. These hairs are further classified into four types, one of which is setose hairs that are characterized as stiff, ferruginous, approximately 0.5 mm long, entirely septate with thick, smooth cell walls. Confined to vegetative parts, setose hairs have an upper part filled with a reddish substance and a swollen basal cell that protrudes from the leaf surface. To date, only two Xanthophytum species, X. capitatum and X. setosum Axelius (Axelius 1990), have been reported to possess setose hairs on their leaves. Therefore, our new taxon represents the third species in this group. Its setose hairs are up to 1.5 mm long, three times as long as those in the other species.
In Xanthophytum, flower morphology varies across species, some species having heterostylous flowers and others having homostylous flowers, with different placements of stamens and stigma, as well as varying hair-ring widths inside the corolla. However, many species remain undocumented due to lack of flowering material (Axelius 1990; Chen and Taylor 2011). According to Axelius (1990), in homostylous species with narrow hair-rings, anthers are positioned at the level of the ring with the stigma positioned just above the ring; for those with broad hair-rings, anthers are positioned at the ring’s upper margin with the stigma clearly above the hair-ring. Most heterostylous species with narrow hair-rings have the anthers positioned at the level of the ring and the stigma positioned clearly above it, while species with broad hair-rings show more variation: the stigma can be positioned above or at the level of the ring, and anthers in brevistylous flowers may be above, at, or below the hair-ring, whereas in longistylous flowers, anthers are usually at the level of the ring. Our specimen, with a broad hair-ring, has the anthers at the upper part and the stigma at the lower part of the ring, similar to brevistylous flowers in other species like X. cylindricum Axelius (Axelius 1990). We thus assume our species is heterostylous, and our studied specimen is likely brevistylous, as we have not encountered longistylous flowers.
Xanthophytum antoanense is morphologically closest to X. capitatum (Valeton 1910), sharing the presence of setose hairs on the abaxial leaf surface and a pedunculate head-like inflorescence. However, the two species can be distinguished by key morphological characteristics as outlined in the diagnosis. Additionally, X. antoanense differs in having ovate, slightly 3 - lobed and 1.7–2.5 cm long stipules (vs. triangular to ovate and c. 0.7 cm long in X. capitatum), 4–6 (vs. c. 3.5) cm long petioles, larger flower heads (c. 2 vs. c. 1.5 cm in diameter), adaxially glabrous and 7–8 mm long calyx lobes (vs. pubescent and c. 0.6 mm long), oblong-lanceolate (vs. triangular) corolla lobes, and brevistylous flowers with 5.3–5.5 (vs. c. 2) mm long stamens and a 2.7–2.8 (vs. c. 1.4) mm long style. Furthermore, the corolla tube of brevistylous flowers in X. antoanense is densely hairy on the upper three-quarters of the inside, whereas in X. capitatum, it has a c. 0.6 mm high ring of hairs in the upper part of the tube.
Xanthophytum setosum is easily distinguishable from the new taxon as it has a paniculate inflorescence. It further differs from the new species in having smaller leaf blades (7–16 cm long in X. setosum vs. 13–24 cm long) with 12–19 (vs. 20–22) pairs of secondary veins, shorter petioles (≤ 4 vs. 4–6) cm long, c. 1 cm long and unlobed (vs. 1.7–2.5 cm long and 3 - lobed) stipules, minute (vs. c. 3.5 mm long) bracts, an adaxially densely pubescent (vs. glabrous) calyx with bluntly triangular and c. 1 mm long (vs. spatulate and 7–8 mm long) lobes, smaller brevistylous flowers (longistylous flowers unknown) with c. 1.8 (vs. 5–5.4) mm long corolla tube and c. 1.2 (vs. 2.4–3) mm long corolla lobes, shorter stamens (c. 2.8 vs. 5.3–5.5 mm long), and a c. 1.2 mm long and glabrous (vs. 2.7–2.8 mm long and apically hairy) style. Finally, the corolla tube in X. antoanense is densely hairy on the upper three-quarters of the inside and glabrous on the outside, whereas in X. setosum, it has a narrow ring of hairs below the throat on the inside and is sparsely hairy on the outside.
The leaf size and shape, head-like pedunculate inflorescence, and spatulate calyx lobes in Xanthophytum antoanense are reminiscent of those in X. attopevense from Laos. However, X. attopevense differs in several key characteristics: it has a cuneate to attenuate (vs. cuneate-oblique in X. antoanense) leaf base, shorter petioles (c. 2 vs. 4–6 cm long), c. 1.5 cm long and unlobed stipules (vs. 1.7–2.5 cm long and 3 - lobed), flower heads c. 1.5 (vs. c. 2) cm in diameter, up to 1.5 (vs. 3.5–4.5) cm long peduncles, adaxially hairy and 1.5–2.5 mm long (vs. glabrous and 7–8 mm long) calyx lobes, a c. 2 (vs. 5–5.4) mm long corolla tube, and c. 1 (vs. 2.4–3) mm long corolla lobes. Notably, X. attopevense was not reported to have setose hairs on its leaf blades, although this type of hair is depicted in a drawing illustrating fruits attached to the type specimens Harmand 1099, collected in February 1877, Attopeu, Bassac, Laos (P, barcodes 02436251 and 02436253) (JSTOR 2024).
The morphological differences among these four species are summarized in Table 1.
description: Published as part of Nguyen, Hieu Cuong, Nguyen-Le, Xuan Bach, Nguyen, Quoc Dat, Nguyen, Tran Quoc Trung & Luu, Hong Truong, 2024, Xanthophytum antoanense (Rubiaceae, Ophiorrhizeae), a new species from Vietnam, pp. 215-222 in PhytoKeys 250 on pages 215-222, DOI: 10.3897/phytokeys.250.137482