Sargassum feldmannii Pham-Hoàng (1967: 297)

Tu, Nguyen Van, 2023, Morpho-anatomical study of Sargassum (Fucales, Phaeophyceae) diversity reveals noteworthy collections and range extensions from southwestern Vietnam, Phytotaxa 600 (5), pp. 281-290 : 285

Sargassum feldmannii Pham-Hoàng (1967: 297) ( Fig. 4A–F )

Thallus 30–40 cm high, attached by a discoidal holdfast that is up to 1 cm in diameter. Main axes cylindrical, short, up to 0.3 cm wide, producing 2–3 primary branches. Primary branches compressed, smooth, 0.3–0.4 cm in diameter; lateral branchs short, raising at an interval of 1–3 cm. Leaves thick, elliptic to linear, 2–3 cm long and up to 1 cm wide, obtuse or rounded at the apex, sometimes double serrated or forming a cup–shape, with short cylindrical petioles, bearing some spines at top. Midribs vanishing near the apex. Cryptostomata numerous, irregularly scattered over leaf surfaces. Vesicles on leaves, spherical to elliptic, normally arranged at the central or distal part of the vesicle–leaves, with sharply dentate margins, 0.6–0.8 cm wide.

Plant monoecious. Receptacles forming dense cymes, branched, cylindrical and warty, up to 0.7 cm long. Maturation likely in late spring in the southwestern Vietnam.

Habitat:— Sargassum feldmannii grows on rocks and dead corals in the subtidal zone in the Phu Quoc and Tho Chu islands.

Specimens examined:— Ganh Dau, Phu Quoc, subtidal, 15 Feb. 2019, V. T . Nguyen ( NVT2461 , NVT2462 ), Bai Dong, Tho Chu, subtidal, 21–23 Mar. 2019, V. T . Nguyen ( NVT2563 , NVT2564 , NVT2634 , NVT2667 , NVT2669 , NVT2670 ) .

Taxonomic remarks:— Sargassum feldmannii is distinguished from other species by having compressed branches, vesicles with terminal leaves that are thick, inwardly curved branches, and serrated margins of leaves. The type locality of this species is Nha Trang, Vietnam ( Pham 1967). It differs from S. aquifolium (Turner) C.Agardh ( Agardh 1820: 12) by its large leaf size, and the shape of its vesicles ( Nguyen 2014). Sargassum feldmannii has short lateral branches, usually curved, thick leaves to stem compared to S. carpophyllum J.Agardh ( Agardh 1848: 304) . Based on morpho-anatomical examination of specimens from Phu Quoc Island, S. feldmannii is distinct from S. crassifolium J.Agardh ( Agardh 1848: 326) , a species currently treated as a synonym of S. aquifolium (type locality, Sunda Strait, Indonesia, Silva et al. 1996).

Figures

FIGURE 4. Sargassum feldmannii Pham-hoang. A. Habit of a voucher specimen (NVT2561). B. Holdfast. C. Leaves. D. Vesicles. E. Receptacles. F. Section of receptacle.