Primulina minima Z.B.Xin & L.F.Fu, 2025

Long, Shu-Ting, Xin, Zi-Bing, Maciejewski, Stephen & Fu, Long-Fei, 2025, Primulina minima, a new species of cave-dwelling Gesneriaceae from the karst landscape of northwestern Guangxi, China, Phytotaxa 696 (4), pp. 294-299 : 295-298

Primulina minima Z.B.Xin & L.F.Fu , sp. nov. ( Figs 1–2 )

Diagnosis: — P. minima resembles P. longzhouensi , P.rufipes and P.huaijiensis in size and color of the corolla, but can be distinguished by the number of inflorescences, 3–5 per plants(vs. P. longzhouensi , 5–10 per plant; vs. P.rufipes , 3–7 per plant; vs. P.huaijiensis , 4–10 per plant), the size of bracts, 1–2 × ca. 1 mm (vs. P. longzhouensi , 4–9 × 1.5–3.5 mm; vs. P.rufipes , 5–10 × 1–3 mm; vs. P.huaijiensis , 2–3 × ca. 1 mm); corolla 7–8 mm long, corolla tube infundibuliform, ca. 5 mm long and outside glandular pubescent (vs. P. longzhouensi , 10–14 mm long, tubular, 8–9 mm long, puberulent only at mouth of corolla tube; vs. P.rufipes , 8–10 mm long, infundibuliform, 5–6 mm long, sparsely pubescent outside, glabrous inside; vs. P.huaijiensis , 7–9 mm long, infundibuliform, 4–6 mm long,sparsely glandular pubescent outside, glabrous inside); lobes apex acute (vs. P. longzhouensi , obtuse; vs. P.rufipes , rotund or obtuse; vs. P.huaijiensis , rounded); ovary ca. 3 mm long (vs. P. longzhouensi , ca. 1.5 mm; vs. P.rufipes , 2 mm; vs. P.huaijiensis , 1.5 mm).

Type: — CHINA. Guangxi Zhuangzu Autonomous Region: cultivated in Guilin Botanical Garden, introduced from Hechi City, Fengshan County, Jinya Town, Daping Village, on moist rock face at the entrance of karst caves, rare, 780 m a.s.l., 11th July 2024, Z. B. Xin et al. XZB240711-01 (holotype: IBK).

Description: —Perennial herb, rosette. Rhizome subterete, 4–15 mm long, 4–5 mm in diameter. Leaves 6–12, all basal, opposite, petiolate; petiole 2–5 cm long, dark green, densely white pubescent; leaf blade fleshy, green adaxially, gray-green abaxially, elliptic to broadly ovate, 2–6 × 2–4 cm at the middle, apex rounded, base cuneate, margin usually entire, occasionally obscurely crenate, densely white puberulent on both sides. Cymes axillary, 3–5 cymes per plant, inflorescence dichasial, 1–3-flowered; peduncle ca. 6 cm long, white pubescent. Bracts 2, opposite, lanceolate, 3 × 1, mm, abaxially sparsely white pubescent, adaxially pubescent, margin entire, apex rounded; pedicels 0.8–3 cm long, 1–2 mm in diameter, white glandular puberulent. Calyx 5-lobed to the base, lobes lanceolate, 4–5 × 0.5–1 mm, outside glandular-puberulent inside sparsely puberulent, margin entire, acuminate, apex obtuse. Corolla white to very pale lilac, 7–8 mm long, outside covered in glandular puberulent, inside nearly glabrous; tube infundibuliform ca. 5 mm long, ca. 3 mm in diameter, ca. 2 mm in diameter, limb distinctly 2-lipped; adaxial lip 2-parted to over the middle, lobes narrowly triangular-ovate, 2–2.5 × 1.5–2 mm, margin entire, apex acute, abaxial lip longer, 3-parted to near the base, the lateral ones narrowly triangular-ovate, ca. 3 × 2 mm, the central one narrowly triangular-ovate, ca. 3.5 × 1.5 mm, margin entire, apex acute. Stamens 2; filaments 3–4 mm long, adnate to corolla tube ca. 1 mm above the base, distinctly geniculate at the middle, pubescent; anthers reniform, distinctly constricted at the middle, ca. 1.5 mm long, pale yellowish brown, glabrous. Staminodes 3, the lateral two obvious, the central one reduced to almost disappear or tiny; the lateral two adnate to ca. 2 mm above the base of the corolla tube, ca. 1.5 mm long, apex capitate, straight, glabrous. Disc annular, ca. 1 mm high, margin entire, glabrous. Pistil ca. 5.5 mm long; ovary green, ovoid, ca. 3 mm long, ca. 1.5 mm in diameter, densely glandular puberulent, style white, ca. 2.5 mm long and ca. 0.5 mm in diameter, densely glandular puberulent. Stigma pale green, chiritoid-like, apex 2-lobed, each lobe ovate, ca. 0.5 mm long, ca. 0.5 mm in diameter at base, apex usually retroflexed with inconspicuous glands on the surface. Capsule light green when young, ovoid, ca. 1 cm long, ca. 0.6 mm in diameter, sparsely white puberulent.

Distribution and Ecology: —So far, it has only been found in the type locality of Daping Village, Jinya Township, Fengshan County, Hechi City, Guangxi, China, and grows on the vertical rock walls at the entrance to large caves in the typical karst landforms. The average annual temperature in Daping Village is 20.6 ° C, and the average annual precipitation is 1456.2 mm.

Phenology: —The flowering period of this new taxon is from June to July. Fruiting time from August to September.

Etymology: —The species epithet “ minima ” comes from the Latin adjective “ minimus ”, which is the superlative of the adjective “ parvu ” and means “very small, minimal”. After conversion, it is used to refer to the species with the very samll corolla among the currently known Primulina plants, which is one of the smallest corolla.

Conservation status: —The author has conducted extensive field surveys near its type locality over the past six years. There are no similar medium-sized to large caves within a limestone mountain area of about 4 square kilometers around the cave on which it depends for survival. The fact that this limestone cave is located in a mountain area surrounded by crop fields near villages suggests that there are serious obstacles to the migration of this species. Therefore, based on the available information, we conclude that the species currently only survives in this large cave, with a very limited population of less than 50 mature individuals. At the same time, the lower part of the cave is used by local residents to store straw and other materials, and there is relatively serious human interference. Therefore, according to the IUCN assessment standard (2024), the species is provisionally assessed as “Critically Endangered” [CR+C2a (i)].

Notes: —This species exhibits one of the smallest corolla among all extant Primulina species. Notably, this trait remains highly stable, showing no variation in flower shape or size despite improved cultivation conditions, providing a clear distinguishing characteristic within the genus.

Primulina minima morphologically resembles P. longzhouensi , P. rufipes and P.huaijiensis , all have white corollas with minor differences in corolla size and petal tips, of which P. minima close to smallest, and they have similar corolla shapes, but they have tiny differences in bract and ovary size.

Flowering occurs from June to July for Primulina minima , contrasting with November to December for P. longzhouensis , P. rufipes flowering from April to May, P.huaijiensis from October to November. A detailed morphological comparison between these species is presented in Table 1.

Figures

FIGURE 1. Primulina minima Z.B.Xin & L.F.Fu sp. nov.—A. Habit..—B. The adaxial and abaxial surfaces of leaf blades.—C. The abaxial surfaces of Bracts, secondary and tertiary bracteoles.—D. The abaxial surfaces of Calyx lobes.—E. The frontal view of corolla.— F.The lateral view of corolla and flower with pedicel.—G. Opened corolla showing stamens and staminodes.—H. Stamens.—I. Pistils without calyx lobes.—J. Stigma. (Drawn by Shu-Ting Long).

FIGURE 2. Primulina minima Z.B.Xin & L.F.Fu sp. nov.—A. Habit..—B. The adaxial and abaxial surfaces of leaf blade..—C. Cymes and peduncles.—D. Bracts.—E. Calyx lobes.—F. Frontal view of corolla.—G. Lateral view of corolla.—H. Open corolla showing stamens and staminodes.—I. Pistils. (Photoed by Zi-Bing Xin).