Pterobryopsis siheiana A.E.D. Daniels & S. Athira

Daniels, A. E. D., Athira, S., Kuznetsova, O. I. & Ignatov, M. S., 2024, Pterobryopsis siheiana (Bryophyta: Pterobryaceae) - a new species from the Western Ghats of India, Phytotaxa 650 (2), pp. 179-184 : 180-183

Diagnosis

Pterobryopsis siheiana resembles P. schmidii , P. acuminata and P. kegeliana in having decurrent leaf base consisting of an alar region made of small quadrate to subquadrate cells. However, the new species differs from all the three in having strongly dimorphic stem and branch leaves and has unique and conspicuous features including the large group of quadrate to subquadrate supra-alar cells which are many more-rowed in both stem and branch leaves than in the other three species, the variable costae in stem and branch leaves, and the strongly differentiated leaf apical cells between stem and branch leaves i.e., long-linear versus short-linear.

Molecular phylogenetic data provide additional support for the independence of the specimen in question, thus we describe it as new to plant science.

Pterobryopsis siheiana A.E.D. Daniels & S. Athira , sp. nov. ( Figure 2 )

— Type: India, Western Ghats , Kerala, Idukki District, Kadamakuzhy, Pottamkulam Estate, ca 1074m, corticolous on Syzygium cumini (L.) Skeels ( Myrtaceae ), in a mixed plantation, 9.7033˚N, 77.1024˚E, 16 October, 2022, S. Athira 326 p. p. (holotype: CAL; isotype: SCCN)

Etymology: Named after the renowned bryologist Dr. Si He of the Missouri Botanical Garden (MO), the USA, for his significant contribution to the Moss Flora of China and, South and Southeast Asian Countries.

Description: Plants yellowish-green. Primary stems creeping, 1–2.5 cm long, wiry, reddish-brown, 0.7–0.75 × 0.58–0.6 mm in cross section, almost circular, without a central strand; cortex 2- or 3-layered; cells 1–4 × 1–3µm, quadrate-hexagonal, thick-walled, reddish-brown; medullary ones 3–8 × 3–9µm, thin-walled; scale leaves ovatespathulate, 0.31–0.32 × 0.21–0.23 mm, entire to faintly crenulate at margin, reddish-brown tinted at base, acute to long acuminate at apex, ecostate. Secondary stems 0.5–1.2 cm tall, erect, 0.64–0.75 × 0.6–0.65 mm in cross section, ovate, without a central strand; cortex 2- or 3-layered; cells 1–7 × 1–6 µm, mostly rounded-hexagonal, highly thick-walled, yellowish-brown; medullary cells 5–10 × 4–9 µm, thick-walled but not as thick as cortical cells. Pseudoparaphyllia scarce, at leaf primordia, 0.19–0.29 × 0.1–0.2 mm, filamentous to subfilamentous. Leaves imbricate, erectopatent, 2.2– 2.5 × 1–1.2 mm; stem leaves ovate to cordate-ovate, concave, vertically plicate, decurrent, faintly crenulate at margin, toothed and acuminate at apex or faintly crenulate and long-apiculate at apex, twisted when long-apiculate; apical cells 20–42 × 3–7 μm elongate-linear, incrassate, pitted; median cells narrow, elongate, 25–40 × 2–3 μm, thin-walled, faintly pitted; those at base 15–30 × 6–9 μm, reddish-brown tinted and pitted at juxta-costal region; supra-alar region made of several rows of 5–30 × 6–10 μm quadrate to subquadrate cells; alar cells at the angles, reddish-brown tinted; costae faint, variable from single in leaves with acute and toothed apex to double or forked in leaves with long-apiculate, faintly crenulate and twisted apex; when double, one shorter; longer one, more than 1/2 as long as leaf; shorter one, 1/2 as long as the longer. Branch leaves imbricate, erectopatent, 1.8–2.1 × 0.8–1.2 mm, oblong-ovate, concave, vertically plicate, but not as strongly as in stem leaves, decurrent, involute and faintly crenulate at margin, roughly cochleate and acuminate at apex, not twisted; apical cells 9–20 × 4–10 μm elongate-hexagonal, thin-walled, faintly pitted; median cells narrow, elongate, 35–46 × 5–7 μm, thin-walled, faintly pitted; those at base 10–16 × 6–12 μm, reddish-brown tinted and pitted at juxta-costal region; alar region made of numerous rows of quadrate to subquadrate cells above the reddish-brown tinted cells in the basal angles; cells 5–12 × 4–9 μm; costa single, 3/4 as long as leaf, faint. Axillary hairs 2–4-celled, 24–50 × 8–10 μm uniseriate. Gemmae 115–205 × 25–30 μm. Sporophyte not seen.

Habitat: Corticolous on Syzygium cumini (L.) Skeels ( Myrtaceae ), in a mixed plantation, ca 1074 m.

Distinctions: The two most unique and conspicuous features of Pterobryopsis siheiana are the presence of a large group of quadrate to subquadrate supra-alar cells and the strongly differentiated leaf apical cells between stem and branch leaves i.e., long-linear versus short-linear. The development of supra-alar region in P. siheiana is much more extensive (almost twice more rows) than in P. acuminata , P. kegeliana and P. schmidii . The dimorphic stem and branch leaves are much more distinctive in the new species than the three species mentioned above. In addition, the cross section of the stems is almost circular in P. siheiana whereas it is ovate in P. acuminata , P. kegeliana and P. schmidii . There are also differences between the new species and the three allied species in the number of layers of cortex and the shape of the cortical cells (2- or 3-layered versus 3–5-layered and rounded-hexagonal versus quadrate-hexagonal). Moreover, the pseudoparaphyllia are filamentous to subfilamentous in P. siheiana whereas they are filamentous to lanceolate in P. acuminata . Certainly, future discovery of the sporophyte of P. siheiana will be helpful in understanding its relationship within the genus Pterobryopsis .

The binomial Pterobryopsis flexipes which was reduced to a synonym of P. schmidii by Noguchi (1987), is resuscitated here as it isolated itself from the P. schmidii and P. divergens clade thereby proving to be a good species and hence included in the key.

Figures

FIGURE 2. (A–W). Pterobryopsis siheiana A.E.D. Daniels & S. Athira.A. Habit B–D. Stem leaves E. Cross section of stem F–G. Branch leaves H. Cross section of branch I. Apical cells of stem leaves J. Apical cells of branch leaves K. Marginal cells of branch leaves L. Median cells of stem leaves M. Median cells of branch leaves N. Basal cells of stem leaves O. Basal cells of branch leaves P.Alar cells Q. Costae of stem leaves R–S Gemmae T. Stem scale leaf U. Branch scale leaf V. Pseudoparaphyllia W. Axillary hairs (from S. Athira 326 pp.)