Petrocosmea albocaerulea B.H.Quang, T.D.Thien & Nuraliev, 2024

Thien, Tran Duc, Quang, Bui Hong, Anh, Tran Thi Phuong, Hai, Do Van & Nuraliev, Maxim S., 2024, Petrocosmea albocaerulea (Gesneriaceae), a new species from northwestern Vietnam, Phytotaxa 678 (3), pp. 193-200 : 194-198

Petrocosmea albocaerulea B.H.Quang, T.D.Thien & Nuraliev , sp. nov. ( Fig. 1 & 2 )

Diagnosis:— Petrocosmea albocaerulea differs from all the other species of the genus by the following combination of characters: leaf blade not peltate, several-flowered inflorescences, corolla glabrous inside, corolla lobes not longer than the tube, glabrous stamen filaments, anthers rounded at the apex, and style hairy near the base and glabrous otherwise. The new species is most similar to P. confluens , differing in having several-flowered inflorescences, corolla with white tube and light blue lobes, and style hairy near the base.

Type:— VIETNAM. Lai Chau Province: Muong Te District, Mu Ca Commune, Mu Ca Protected Forest , 22°34’09.7’’N, 102°25’46.1’’E, elev. ca. 300 m a.s.l., 22–28 May 2018, B. H. Quang 212 [fl.] (holotype HN HN00008070 !; isotypes HN HN00008071 !, HN00008072 !) .

Description:— Plant lithophytic, perennial, herbaceous, rhizomatous, acaulescent. Rhizome 5–10 mm long. Leaves rosulate, 10–12 per aerial shoot. Petiole 10–11(–40) mm long, green, pilose. Leaf blade broadly ovate to orbicularovate, 10–25 mm long, 10–20 mm wide, succulent, adaxially green, abaxially pale green, base cordate with overlapping margins, symmetric or slightly asymmetric, margin shallowly crenate, apex obtuse to rounded; adaxial side densely pilose, pustulate at bases of hairs; abaxial side densely pilose and also with white glandular trichomes on the veins; secondary veins 4–5 on each side of midvein; midvein and secondary veins adaxially slightly impressed, abaxially raised. Inflorescences 10–20 per shoot, axillary, cymose, 3–8-flowered; peduncle ascending, 4–5 cm long, densely glandular pilose and sparsely villous; bracts (subtending 2 main branches) opposite, linear, about 2–3 mm long, sparsely glandular pilose on both surfaces. Calyx zygomorphic, green with dark reddish base, densely glandular pilose outside (with some hairs reaching length of 3 mm or even longer) and sparsely glandular pilose inside, unequally divided into5 lobes; adaxial sepal united with the neighboring sepals for about 1/3 of calyx length (ca. 1 mm), and otherwise calyx lobed nearly to base; lobes more or less appressed to corolla, narrowly triangular, with acuminate apex; 3 adaxial lobes 2–3 mm long and 1.0– 1.4 mm wide at base, 2 abaxial lobes 3–4 mm long and 1.4–1.5 mm wide at base. Corolla zygomorphic, with white tube and light blue lobes (outside and inside), inside usually with 2 yellow spots on abaxial side (beneath the anthers), bilabiate and pronouncedly oblique due to abaxial lip being longer than adaxial lip, 8–9 mm long, shortly glandular pubescent outside and along lobe margins, glabrous inside; tube 4–5 mm long, abaxially gibbous (inflated); adaxial lip 1.5–2.0 mm long, shortly 2-lobed, lobes semicircular, 0.5–1.2 × 1.5–1.6 mm, slightly reflexed (bent backward); abaxial lip ca. 3–5 mm long, 3-lobed, lobes broadly ovate with rounded apex, 3–4 × 4.5–5 mm, spreading. Stamens 2 (anterior pair), attached at base of corolla tube, free from each other, glabrous; filaments white, straight, narrowly triangular, 1.0– 1.5 mm long, 0.5–0.7 mm wide at base, slightly curved near middle; anthers deeply included in corolla tube, ovate, rounded at apex, 1.5–1.8 × 0.5–1.0 mm, dorsifixed; thecae parallel, mode of dehiscence unknown. Staminodes 3, minute and inconspicuous, attached at base of corolla tube, glabrous. Disk absent. Pistil 4–5 mm long; ovary superior, green, conical, ca. 1–2 mm long, 1–1.5 mm in diameter, densely glandular pilose; style appressed to adaxial side of corolla, white, linear, straight or apically slightly bent downwards, 2–3.5 mm long, 0.1–0.2 mm in diameter, sparsely glandular puberulent near base and glabrous otherwise; stigma slightly exerted from corolla tube, white, capitate, 0.2 mm in diameter, glabrous. Fruit unknown.

Distribution:— Vietnam (Lai Chau Province: Mu Ca Protected Forest; Dien Bien Province: Muong Nhe Nature Reserve).

Ecology and phenology:— The species inhabits primary evergreen forests at elevations of 300–500 m, where it occupies vertical cliffs along streams and rivers. Flowering from May to August.

Etymology:— The specific epithet “ albocaerulea ” refers to the corolla coloration of the new species, as it is characterized by white tube and blue lobes. This pattern makes the new species distinct from many of its congeners.

Additional specimens examined (paratypes):— VIETNAM. Lai Chau Province: Muong Te District, Mu Ca Commune, Mu Ca Protected Forest , 22°34’08.6’’N 102°25’45.1’’E, elev. ca. 300 m a.s.l., 6 August 2018, B. H. Quang 226 [fl.] ( HN HN00008073 , HN00008074 , HN00008075 ) ; Dien Bien Province: Muong Nhe District, Muong Nhe Nature Reserve , 22°13.714’N 102°22.798’E, elev. 500 m a.s.l., 8 August 2023, B. H. Quang, V. A. Thuong, T. D. Thien, P. D. Chinh, N. T. Thanh, D. V. Hai, T. D. Binh TQA-357 [fl.] ( HN HN00008076 , HN00008077 , HN00008078 , HN00008079 , HN00008080 ) .

Notes on sectional subdivision of Petrocosmea :— In the most recent revision of Petrocosmea performed by Qiu & Liu (2015), the genus is subdivided into five sections. These sections correspond to the five major clades recognized within the genus in the molecular phylogenetic study by Qiu et al. (2015). The system suggested by Qiu & Liu (2015), however, contains several nomenclatural inconsistencies that are to be resolved to make the system appropriate for taxonomic usage.

First, the two sections introduced in the revision are invalid, because their types were not indicated (Art. 40.1 and 40.6 of ICN: Turland et al. 2018): they are Petrocosmea sect. Barbatae Z.J.Qiu in Qiu & Liu (2015: 160) and Petrocosmea sect. Minor Z.J.Qiu in Qiu & Liu (2015: 87).

Second, Petrocosmea sect. Minor is circumscribed by Qiu & Liu (2015) to include the type species of Petrocosmea sect. Anisochilus Hemsley (1899a : Pl. 2599), i.e., P. iodioides Hemsley (1899a : Pl. 2599) (designated by Wang 1985). Consequently, the correct name of this species group at the sectional rank is Petrocosmea sect. Anisochilus . The name Petrocosmea sect. Minor is therefore superfluous, in addition to being invalid (Art. 52.1 and 52.2(a) of ICN: Turland et al. 2018).

Finally, within the species group named by Qiu & Liu (2015) as Petrocosmea sect. Anisochilus , none of the species is a type of any sectional name. Thus, a new name is to be established in order to recognize this group at a rank of a section.

Taxonomic affinities of Petrocosmea albocaerulea :— Within the classification and identification key provided by Qiu & Liu (2015) and Qiu et al. (2015), Petrocosmea albocaerulea falls within clade B (incorrectly named by Qiu & Liu (2015) as sect. Anisochilus ). This is evident from the anthers of the new species being rounded (not constricted) at the apex, corolla lobes not longer than the tube, and mostly glabrous style (hairy only near base). Additionally, P. albocaerulea fits clade B in the following characters outlined by Qiu et al. (2015): acaulescent plant habit with leaves forming a rosette, abaxially inflated corolla tube, adaxial to abaxial lip ratio of about 1:2, adaxial lip lacking a longitudinal folding (not plicate), somewhat reflexed adaxial corolla lobes, style appressed to adaxial side of corolla (and accordingly, placed above anthers), and distal part of the style bent downwards.

Petrocosmea albocaerulea differs from all the other species of clade B in the following combination of morphological traits: leaf blade not peltate, several-flowered inflorescences, corolla glabrous inside, and glabrous stamen filaments. Within the key provided by Qiu & Liu (2015), the new species appears to be most close to P. confluens Wang (1984: 9) , differing from it in having 3–8-flowered (vs. single-flowered) inflorescence, corolla with white tube and light blue lobes (vs. uniformly blue to violet), and style puberulent near base (vs. entirely glabrous). In addition, P. albocaerulea is remarkably similar to P. intraglabra ( Wang 1985: 57) Z.J.Qiu in Qiu & Liu (2015: 76) in the overall plant appearance and flower coloration, but differs from the latter in having 3–8-flowered (vs. single-flowered) inflorescence, glabrous (vs. puberulent) stamen filaments, and somewhat shorter style (2–3.5 mm vs. ca. 5 mm long). The detailed comparison between these three species is provided in Table 1.

Figures

FIGURE 1. Petrocosmea albocaerulea, general morphology. A. Plant with flower buds. B. Plant with flowers. C. Leaf (abaxial view). D. Inflorescence with the first anthetic flower. E. Excavated plant (view from below). Quang 212. Photos by H.Q. Bui, correction and design by M. Nuraliev.

FIGURE 2. Petrocosmea albocaerulea, floral morphology. A, B. Flowers (front view). C. Inflorescence. D. Abaxial lip of corolla with stamens. E. Flower bud (side view). F. Flower (side view). G. Stamens. H. Base of corolla with stamens and staminodes (indicated by arrows). I. Stamen (adaxial view). J. Pistil (side view). Quang 212. Photos by H.Q. Bui, correction and design by M. Nuraliev.