Sedum formosanum N.E. Brown., subsp. miyakojimense Takuro Ito, Yokota & Kokub., 2020

Ito, Takuro, Yu, Chih-Chieh, Yokota, Masatsugu & Kokubugata, Goro, 2020, Sedum formosanum subsp. miyakojimense (Crassulaceae), a new subspecies from Miyako-jima Island of the Ryukyu Islands, Japan, PhytoKeys 148, pp. 51-70 : 51

Sedum formosanum N.E. Brown., subsp. miyakojimense Takuro Ito, Yokota & Kokub. subsp. nov. Figs 3A-D , 4

Type.

Japan. The Ryukyus: Miyako Islands, Miyako-jima Island, Gusukube, 5 April 2015, Takuro Ito 2402 (holotype: TNS)

Diagnosis.

Sedum formosanum subsp. miyakojimense differs from its close relative S. formosanum subsp. formosanum in being perennial, polycarpic, and having lateral branches arising from the leaf axils.

Description.

Perennial herb, fleshy, glabrous. First year stem stout, erect, partly woody, 1-5 lateral branches in the leaf axils, 3-10 cm tall, with lax rosettes; rosettes 2.5-6 cm wide with 7-15 leaves. Flowering stems fleshy, 10-20 cm tall, base ca. 5 mm broad, yellowish green, erect or sprawling and creeping at base. Roots fibrous, sometimes adventitious at the leaf scar. Leaves alternate, occasionally verticillate, sessile, green or yellowish, flattish, ± thick, spatulate to oblanceolate, 1.1-3.1 cm long, 0.3-1.0 cm wide, apex rounded, base long, attenuate, margins entire. Inflorescences terminal, cymes, basically trifurcate with 3 primary axes, sometimes with 2, 4, or 5 primary axes; primary axis 2-8 cm long, ascending, 1 to several times irregularly and often unequally forking, with a flower at each fork, ultimate branches 1-2 cm long, 3-7 flowered; bracts leaf-like, smaller than cauline leaves. Flowers 5 (rarely 6)-merous, 7-11 mm wide, sessile. Sepals 5, free, yellowish green, fleshy, flattish, unequal in size, obovate to oblanceolate, 1.8-4.5 mm long, 1.2-3.3 mm wide, apex round or obtuse, base spurred. Petals 5, bright yellow, lanceolate, 4.6-6 mm long, 1.3-1.6 mm wide, apex acuminate, base slightly connate. Stamens 10, shorter than petals, 4.2-5 mm long, erect at flowering, two-whorled arrangement; anthers oblong-lanceolate, ca. 0.5 mm long, deep yellow before dehiscence. Pistils 5, 5.2-6.3 mm long; carpels 5, free, connate at the base, gibbous ventrally. Fruits star-shaped, follicle, erect, 5.3-6.8 mm long. Flowering in April to June.

Taxonomic note.

This new subspecies is classified in the sect. Sedum because of its adaxially gibbous carpels ( Fu and Ohba 2001) (Fig. 3 ).

Etymology.

The epithet refers to the Japanese name of the type locality.

Distribution and habitat.

Endemic to the southeastern portion of Miyako-jima Island (The Ryukyus), on sunny, coastal limestone.

Additional specimens examined.

Japan. The Ryukyus: the Miyakojima Islands, Miyako-jima Island, Gusukube, 5 April 2015, Takuro Ito 2403, 2408 (isotype: TNS).

Conservation.

IUCN Red list category: Critically Endangered (CR). The distribution of Sedum formosanum subsp. miyakojimense is restricted to only one location ca. 0.15 km2 in Miyako-jima Island, the Ryukyu Islands. The population of the species contains fewer than 200 mature individuals. The plant occurs on limestone rocks scattered in a private golf course, therefore, it is not formally protected. In the future, the population could become threatened, given ongoing land development for tourism in the Ryukyus. Because of the small population size (≤ 250 mature individuals) and small area of occupancy (≤ 10 km2), S. formosanum subsp. miyakojimense is classified as CR ( IUCN 2019).

Japanese common name.

Miyako-hama-mannen-gusa (nov.).

Figures

Figure 3. Sedum formosanum subsp. miyakojimense (A-D T. Ito 2402, 2408, Miyako-jima Island of the Ryukyus, Japan) and S. formosanum subsp. formosanum (E Kume-jima Island of the Ryukyus, Japan. F, G NewTaipei City, Taiwan). A, B, E habit C, F flower D, G leaf. Scale bars: 1 mm (D-F).

Figure 4. Sedum formosanum subsp. miyakojimense. A flower B sepal C leaf, adaxial D leaf, abaxial E habit. Scale bars: 1 mm (A-D); 1 cm (E). Line drawings by Naomi Kizaki.