Mitreola capitata Nuraliev

Nuraliev, Maxim S., Lyskov, Dmitry F., Kuznetsov, Andrey N., Kuznetsova, Svetlana P. & Fu, Long-Fei, 2023, Novelties in Asian Mitreola (Loganiaceae): M. capitata, a new species from Vietnam, and lectotypification of M. spathulifolia, Phytotaxa 585 (1), pp. 39-47 : 40-44

Mitreola capitata Nuraliev ( Fig. 1–3 )

Diagnosis: — Mitreola capitata is unique among the species of the genus Mitreola in having the following combination of characters: short stem with rosulate leaves, hairs on leaves and peduncle and a capitate inflorescence with a long peduncle. It is most close to M. spathulifolia , differing in leaves 5.9–12 cm long, a dense capitate inflorescence 0.8–2.3 cm in diameter when flattened, pedicel ca. 0.5 mm long, hairy calyx, and capsule 2 mm long and 2–2.5 mm wide.

Type: — VIETNAM. Quang Binh Province: Bo Trach District, Tan Trach commune, Phong Nha-Ke Bang National Park , limestone rock, 17°24’41’’N 106°13’59’’E, elev. 650 m, 30 March 2022, Nuraliev M. S ., Lyskov D. F ., Dac L . X., Ha L. M ., Thang D. Q. NUR 3614 (holotype: MW: MW0595774 ; isotype: MW: MW0595775 ) .

Description:—Herb lithophytic, perennial. Stem rhizome-like, ascending to vertical, to 4 cm long, ca. 5 mm in diameter (in old plants), branched in old plants, pubescent with dense spreading white hairs ca. 0.3 mm long when young; internodes usually vanishingly short, in young shoots up to ca. 4 mm long, rarely up to 12 mm long especially in lateral branches; plant with tap root up to ca. 1.5 mm in diameter at base, at basal portion of stem (with leaves withered) sometimes with thin adventitious roots ca. 0.4 mm in diameter. Stipules interpetiolar, flange-like to scalelike, in latter case broadly triangular to ovate, up to ca. 1 mm long and 2 mm wide, glabrous; nodes in axils of stipules and leaves bearing numerous narrowly clavate gland-like papillae (colleters) ca. 0.5–1 mm long with blackish apices. Leaves rosulate, opposite, equal in each pair, sessile; leaves persistent in several distal nodes of each shoot. Leaf blade chartaceous in sicco, obovate (to broadly oblanceolate), adaxially dark green with a distinct whitish green midvein in vivo, abaxially pale green in vivo, both sides brownish green in sicco, larger blades on each shoot (5.9)7.0–11.0(12.0) cm long and (2.6)2.9–4.4(5.2) cm wide, (1.6)1.8–3.7 times as long as wide; base cuneate to nearly attenuate; apex very broadly acute to obtuse or almost rounded; margin entire, ciliate with white hairs up to 0.5 mm long; both surfaces pubescent with dense erect white hairs ca. 0.5 mm long; midvein ca. 0.8–1 mm wide at base, gradually becoming thinner towards apex; secondary veins pinnately arranged, 6–7(8) on each side of midvein, ascending; midvein and secondary veins adaxially slightly impressed, abaxially prominently raised; tertiary veins conspicuous on both sides. Inflorescences evidently terminal, possibly also in axils of upper leaves; peduncle erect, green, 8.5–19.5 cm long, covered with dense spreading white hairs 0.5 mm long. Inflorescence an umbel-like thyrsoid with several cymes (cymes mostly dichasial proximally and monochasial distally), or umbel of such thyrsoids, dense, capitate (head-like), ca. 1.0–2.0 cm in diameter (0.8–2.3 cm when flattened), with numerous congested flowers; all axes similar to peduncle but thinner and with shorter hairs. Bracts appressed to axes, narrowly triangular, green, basal ones (1.5)2.0–2.5(3.0) mm long and 0.4–1.0 mm wide at base, distal ones gradually becoming smaller, adaxially glabrous, abaxially sparsely to densely hairy, with acute apex and slightly serrate margin; small hairy colleters usually present near bract bases. Flower actinomorphic, 5-merous (except for gynoecium). Pedicel ca. 0.5 mm long (rarely flower sessile), with spreading white hairs. Calyx cupuliform-campanulate, 1.5–1.8 mm long, externally (abaxially) covered with sparse spreading white hairs, internally (adaxially) glabrous; tube green, 0.6–0.7 mm long; lobes triangular, green with greenish white margins and apex, 0.7–1.2 mm long, 0.9–1.2 mm wide at base, with acute apex and minutely ciliate margin. Corolla urceolate, white, somewhat translucent in proximal half, ca. 2.8–3.2 mm long and ca. 3.5 mm in diameter when fully open; tube 2.0– 2.5 mm long, 2.0 mm in diameter; lobes horizontally spreading and somewhat curved outwards, imbricate in bud, broadly triangular, 1.0– 1.1 mm long, 0.7–0.9 mm wide at base, with obtuse apex and entire margin; corolla inside with a circular thickening at level of lobe bases bearing a horizontal row of uniseriate multicellular trichomes 0.6 mm long; trichomes pointing at ca. 45° upwards, forming a conical structure and completely obstructing the orifice of the corolla tube; corolla otherwise glabrous. Stamens included in corolla tube, glabrous; filaments inserted at middle of corolla tube, slender and slightly narrowing towards apex, white, ca. 0.4 mm long, pointing at ca. 45° upwards; anthers dorsifixed, ovate, pale yellow, 0.2 mm long, arranged at level of stigmas, introrse. Gynoecium green, glabrous; ovary superior, 2-locular with axile placentation, broadly conical, 0.2 mm long, 0.7–0.8 mm in diameter at base, each locule bearing about 20 ovules; styles 2, tightly connivent with each other into a common style; common style included in corolla tube, very narrowly conical, ca. 0.8 mm long; common stigma capitulate. Fruit (capsule) 2 mm long, 2–2.5 mm wide, glabrous, laterally slightly compressed, bilobed at distal 1/2, lobes divergent, dehiscent along ventral sutures of lobes, bearing persistent calyx ca. 1 mm long (when withered). Seeds several per fruit, black, ca. 0.5 mm in diameter.

Etymology: —The specific epithet “ capitata ” refers to head-like inflorescences which distinguish the new species from all its congeners.

Phenology: —On 30 March 2022, the plants were in full flower, and also bore completely withered fruiting inflorescences (with dehisced capsules) of the previous season.

Distribution and ecology: —The new species is currently known from a single location in Phong Nha-Ke Bang National Park, Vietnam. The species inhabits a prominent outcrop of limestone karst at elevation of 650 m a.s.l., where it occurs in crevices and on vertical walls. Several dozens of individuals were observed.

Mitreola capitata is associated with the dominant tree species Calocedrus rupestris Aver., T.H.Nguyên & L.K.Phan (Cupressaceae) and the herbs including Selaginella sp. (Selaginellaceae) , Amorphophallus glossophyllus Hett. (Araceae) , Ophiopogon sp. (Asparagaceae) , Polygala umbonata Craib (Polygalaceae) , Elatostema spp. (Urticaceae) , Begonia sp. (Begoniaceae) , Strobilanthes sp. (Acanthaceae) and various ferns.

Taxonomic relationships: — Mitreola capitata is readily distinguishable from most of its congeners by short stem with rosulate leaves, presence of indumentum (especially the hairs on leaves and peduncle) and compact longpedunculate inflorescence. Among the previously described species of Mitreola , this combination of features is only found in M. spathulifolia endemic to Daxin and Mashan counties of Guangxi, China. Apart from the habit, the two species share confinement to limestone cliffs. The air distance between the type location of M. capitata and the nearest reported population of M. spathulifolia (its paratype from Daxin: Fang, Zeng 195) is about 590 km.

The main morphological differences between M. capitata and M. spathulifolia are summarized in Table 1 . Most important of them are the leaf length (5.9–12 cm vs. 7–28 cm), size and appearance of inflorescence (0.8–2.3 cm in diameter when flattened, dense and capitate vs. 2–5 cm in diameter when flattened, quite lax), pedicel length (ca. 0.5 mm vs. 1–2 mm), calyx indumentum (hairy vs. glabrous) and capsule size (2 mm long, 2–2.5 mm wide vs. 3 mm long, 5 mm wide). The inflorescence appearance, although not described in the protologue of M. spathulifolia , seems to be especially useful for field recognition of this species against M. capitata : the lax inflorescences are evident from the photos provided by Huang (2007) and presented in this study ( Fig. 4B ).

Figures

FIGURE 1. Mitreola capitata. A, B. Habit. C. Leaf-rosette viewed from below, showing distal portion of stem and abaxial sides of leaves. D. Leaf, adaxial side. Nuraliev et al. NUR 3614. Photos by M.S. Nuraliev.

FIGURE 2. Mitreola capitata. A–C. Inflorescences (top view, side view and view from below). D–F. Flower (top view and oblique views). G. Longitudinally dissected flower. H. Flower (side view). Nuraliev et al. NUR 3614. Photos by M.S. Nuraliev.

FIGURE 3. Mitreola capitata. A. Plant in situ with one anthetic and one fruiting (withered) inflorescence. B–E. Fruiting inflorescence and individual capsules in herbarium material (collected in withered condition). Nuraliev et al. NUR 3614. Photos by M.S. Nuraliev.

FIGURE 4. Mitreola spathulifolia. A, B. Plants in situ with fruiting (withered) inflorescences. C. Population on a limestone cliff. Chi, Fu s.n. (China, Guangxi, Mashan County, Guling Town, Liming Village, Neigan Tun, Neigan Cave, 23°35’20.84’’N 108°22’23.95’’E, 329 m, 04 January 2022). Photos by X. Chi.