Phaeoceros stenothallus Suwanmala & Chantanaorr., 2025

Phaeoceros stenothallus Suwanmala & Chantanaorr. sp. nov.

Figs 8 View Figure 8 , 9 View Figure 9 , 11 C – F View Figure 11

Type.

Thailand • Chiang Mai: Chiang Dao, Denya Khad , 1,413–1,500 m, 14 Nov 2020, S. Chantanaorrapint & O. Suwanmala 4086 ( holotype: PSU!, isotype: NICH!, QFA!) .

Diagnosis.

Phaeoceros stenothallus is similar to P. himalayensis and P. kashyapii but differs in dioicous sexuality, a narrow thallus never broader than 3 mm, wide and the vermiculate spore with hump-like projection on distal face.

Description.

Thallus bright to dark green in fresh material, becoming yellowish green to brown when dry, growing prostrate with loosely to moderately adhering to substrate, forming irregular patches or colonies, compactly, irregularly dichotomous branched into several lobes, thallus lobe strap-shaped, narrow, sometimes tapering toward apex, become boarder in sporophyte-bearing thalli, up to 12 mm long, 0.8–3 mm wide. margins entire to wavy, rarely crenulate, usually flat; apex usually attenuate, gradually tapering into apical tuber, sometimes shallowly lobulate; tubers always present, occurring at apex, along margins, and on the ventral surface, well-developed stalk, the tip with rounded end or ovoid to globose node, sometimes branched, up to 10 mm long. Thallus in cross section biconvex or plano-convex, with 6–16 cells thick in the middle region. Dorsal epidermal cells irregular pentagonal to heptagonal, 23–105 × 18–50 µm. Chloroplasts 1 per cell, occupying nearly entire to half of cell size, frequently contracted into round shape, occasionally folded at margin or star-like shape. Nostoc colonies irregularly distributed, sparse, appearing as dark spots. Rhizoids sparse to densely scattered along the middle region of ventral surface, hyaline to brown. Sexuality dioicous. Androecia abundant at the middle of thallus, distinctively raised over the dorsal surface of thallus, usually 2–3 antheridia per chamber; antheridia subglobose to globose, 2 - tiered stalk with quadriseriate cells, 220–240 × 150–180 µm. Archegonia not seen. Involucres erect, conical-cylindrical, up to 2 mm long, 2–5 cells thick, mouth smooth to shallowly crenulate. Sporophytes often, capsules erect with slightly bending tip, cylindrical, 5–10 (– 12) mm long; epidermal cells of capsule elongate-rectangular, 80–207 × 10–31 µm, thick-walled; stomata 85–92 × 50–54 µm, surrounded by 6–7 cells; assimilative layer 3–5 (– 6) cells thick in cross section; the innermost capsule cells subquadrate to rectangular, 30–110 × 20–38 µm, brown to dark brown; columella consisting 8–16 cells in cross section, reddish brown to dark brown. Spores yellowish brown to dark brown, 29–38 µm in equatorial diameter; distal face hump-like projection without verrucose; proximal face with distinct thin triradiate mark; ornamentation finely vermiculate throughout the spore. Pseudoelaters thin to thick-walled, rarely branched, 1–2 celled; pseudoelaters cells rectangular, brown to dark brown, without helicoidal band.

Etymology.

The epithet “ stenothallus ” refers to the narrow thallus.

Habitat and ecology.

Phaeoceros stenothallus grows abundantly in open areas in mixed deciduous dipterocarp forest and pine-oak forest at elevations between 1,000 and 2,200 m in elevation.

Distribution.

Endemic to Thailand.

Conservation status.

Phaeoceros stenothallus has been found in the north to northwestern part of Thailand, with abundant populations in Chiang Dao Wildlife Sanctuary and spare populations in Mon Long, Doi-Suthep Pui National Park, and Umphang Wildlife Sanctuary. The EOO is estimated to be about 4900 km 2 and the AOO is 36 km 2. The majority of its habitats are unique, occurring in moist but seasonally dry forests, typically on limestone bedrock areas. The species has a risk of habitat disturbance due to human activities and grazing, which may degrade the quality and stability of its natural environment. Therefore, P. stenothallus is here suggested to be Endangered according to IUCN Red List criteria B 1 ab (iii) + B 2 ab (iii) ( IUCN 2024).

Specimens examined.

Thailand • Chiang Mai: Chiang Dao, Doi Sam Phi Nong , 10 Oct 2019, S. Chantanaorrapint & O. Suwanmala 3895, 3896 ( PSU) ; • Denya Khad station to Dong Noi , 19°22'35.38"N, 098°50'06.41"E, 1,413–1,500 m elev., 6 Sep 2012, S. Chantanaorrapint, J. Inuthai & C. Promma 1573 ( PSU) GoogleMaps , 10 Nov 2016, S. Chantanaorrapint & O. Suwanmala 604, 605 ( PSU) GoogleMaps , 10 Oct 2019, S. Chantanaorrapint & O. Suwanmala 3902, 3904, 3907 A ( PSU) GoogleMaps , 14 Nov 2020, S. Chantanaorrapint & O. Suwanmala 4083, 4084, 4086 ( PSU) GoogleMaps ; • Muang Kong - Wiang Haeng boarder , 19°28'N, 098°41'E, 814–825 m elev., 29 Oct 2018, S. Chantanaorrapint & O. Suwanmala 3453, 3456 ( PSU) GoogleMaps ; 6 Oct 2019, S. Chantanaorrapint & O. Suwanmala 3845, 3846 ( PSU) GoogleMaps ; • Na Lao Village , 16 Oct 2020, S. Chantanaorrapint & O. Suwanmala 4073, 4075 ( PSU) GoogleMaps , 3 Oct 2021, S. Chantanaorrapint & O. Suwanmala 4098 ( PSU) GoogleMaps , 19°24'42.47"N, 098°49'57.33"E, 1,089 m elev., 7 Oct 2019, S. Chantanaorrapint & O. Suwanmala 3850, 3853 ( PSU) GoogleMaps ; • the road to Chiang Dao trail , 19°19'55.95"N, 098°54'32.65"E, 807 m elev., 7 Oct 2019, S. Chantanaorrapint & O. Suwanmala 3855, 3860, 3861 ( PSU) GoogleMaps ; • Mae Rim, Mon Long , 18°55'11.27"N, 098°50'25.00"E, 1,350 m elev., 4 Oct 2021, S. Chantanaorrapint & O. Suwanmala 4104, 4106 ( PSU) GoogleMaps ; • Tak: Umphang, Doi Mamuang Sam Muen , 15°52'03.44"N, 098°37'09.80"E, 1,119 m elev., 26 Sep 2020, S. Chantanaorrapint & O. Suwanmala 4048, 4054 ( PSU) GoogleMaps .

Taxonomic notes.

Phaeoceros stenothallus can be distinguished by a combination of the following characters: 1) dioicous sexuality, 2) a narrow thallus never broader than 3 mm wide, 3) the presence of long-stalked tubers on the ventral side, margins, and apex of the thallus, 4) the yellowish brown to dark brown sporophyte at maturity with an adhering valve tip, and 5) the vermiculate spore with a hump-like projection on the distal face.

Phaeoceros stenothallus may be confused with P. himalayensis and P. kashyapii when they are sterile, with a linear and forked thallus. However, P. stenothallus differs from both species by its dioicous sexual condition and the absence of verrucae on the distal face of the spores. Furthermore, this species resembles members of the genus Phymatoceros (especially P. bulbiculosus (Brot.) Stotler et al. and P. phymatodes (M. Howe) R. J. Duff et al. ) in general appearance, such as its narrow thallus, long-stalked tubers, dioicous gametophytes, and spore morphology. However, members of Phymatoceros differ from the new species by their larger spores, thicker-walled epidermal cells of the capsule, and tubers arising from apical cells.