Didymoglossum radiatum S. Chokrassameehirun, Kraichak & Jaruwatt., 2025

Didymoglossum radiatum S. Chokrassameehirun, Kraichak & Jaruwatt. sp. nov.

Figs 2 View Figure 2 , 3 View Figure 3 , 6 A – C View Figure 6

Type.

Thailand • Yala: Waeng District, Hala – Bala Wildlife Sanctuary , 5°47'N, 101°49'E, c. 112 msl., 25 Mar. 2024, S. Chokrassameehirun 24-259 (holotype: BKF; isotype: QBG) GoogleMaps

Diagnosis.

Didymoglossum radiatum is similar to D. tahitense (Fig. 6 D – F View Figure 6 ) and D. hildebrandtii (Kuhn) Ebihara & Dubuisson in having peltate fronds but differs in several key characters. In D. tahitense and D. hildebrandtii , the false veinlets are branched, forming dichotomous branching in almost all veins (Fig. 6 E View Figure 6 ). In contrast, the false veinlets of D. radiatum are parallel, unconnected from the inner base of the false veins throughout their entire length. The frond diameter of D. radiatum is smaller (c. 1.5 cm) compared to D. tahitense (c. 1–3 mm) (Fig. 6 D View Figure 6 ). The sori of D. radiatum are raised, solitary, c. 2 mm long, usually sunk in the deep notch of the fronds. In comparison, the sori of D. tahitense can reach up to 4 mm in length and are situated in shallow marginal notches (Fig. 6 F View Figure 6 ), whereas D. hildebrandtii has multiple sori per frond. Additionally, D. hildebrandtii is distributed in the Comoros and East Africa, unlike D. tahitense , which occurs sympatrically with D. radiatum in the Malesian region. A closely related species, D. beccarianum , is readily distinguished by its stipitate fronds, pinnate arrangement of false veinlets, and sori in the apical notch of fertile fronds.

Description.

Rhizomes: long-creeping, slender, c. 0.2–0.3 mm in diameter, densely covered with dark brown hairs, tightly attached to substrate. Fronds: sessile, peltate, c. 1–1.5 cm in diameter, circular to elliptic, margin of fronds densely covered with short dark brown hairs. False veinlets: dense, connected to joint of fronds, parallel and not connected to each other, running straight to margin, obsolete near apex, densely covered with dark brown hairs underside, and tightly attached to substrate. Sori: solitary, usually one per frond, sunk in deeply notch, borne on main veins running straight from joint of frond, raised, ascending to erect, anticlinal to substrate. Involucres: tubular, c. 2–2.5 mm long, fully emerging from fronds, wings very narrow, forming ridge in appearance, broadly dilated at apex. Receptacles: filiform long exerted.

Distribution and habitat.

This species is only known from Thailand, adjacent to Malaysia. Sparse populations were discovered near the type locality in a nationally conserved area. Epiphytic or epilithic habit, usually near the streamlet at low elevations of lowland evergreen forest.

Etymology.

The specific epithet – radiatum refers to the radiate and parallel arrangement of false veinlets on the fronds.

Vernacular name.

The Thai name “ Fern Bai Bang Rat Sa Mi ” (เฟ ิ นใบบางร ั ศม ี) relates to the specific epithet.

Additional specimens examined.

Thailand • Yala: Waeng District, Hala – Bala Wildlife Sanctuary, Ai Ka Ding canal , c. 190 msl., 24 Mar. 2024, S. Chokrassameehirun 24-241 ( BKF) .