Sedum danjoense Takuro Ito, H. Nakanishi & G. Kokub., 2017

Ito, Takuro, Nakanishi, Hiroki, Chichibu, Yoshiro, Minoda, Kiyotaka & Kokubugata, Goro, 2017, Sedum danjoense (Crassulaceae), a new species of succulent plants from the Danjo Islands in Japan, Phytotaxa 309 (1), pp. 23-34 : 31-32

Sedum danjoense Takuro Ito, H. Nakanishi & G. Kokub. , sp. nov. ( Fig. 3 )

Type:— JAPAN. The Kyusyu, the Danjo Islands, Yorishima Island, 25 October 2016 (cultivated in Nagasaki Subtropical Botanical Garden after collecting its natural habit in 1989), Takuro Ito 3658. (holotype TNS!).

Description:— Biennial herb, fleshy, glabrous. Roots fibrous adventitious at the basal node of each branch. Stem stout, erect with irregular branching, 10–25 cm tall. Leaves mostly alternate, sessile, thick, spatulate to obovate, 1.2–3.2 cm long, 0.5–1.6 cm wide, apex rounded, base long, attenuate, margins entire. Flowering stems fleshy, 10–20 cm tall, base ca. 5 mm broad, usually yellowish, erect or sprawling with irregular branching at base. Inflorescences terminal cymes, flowers usually 10–22 sparsely distributed per branch. Sepals 4, free, green-yellow, fleshy, equal in size, narrowly triangular, 1–3 mm long, 0.8–1.2 mm wide, apex round or obtuse. Petals 4, blight yellow, lanceolate 5–6 mm long, 1.4– 1.7 mm wide, apex acuminate, base slightly connate. Stamens 8, shorter than petals, 4.8–5 mm long, erect at flowering, 2- whorled arranged; anthers oblong, ca. 0.5 mm long, red before dehiscence. Carpels 4, free, horizontal, connate at the base, gibbous ventrally, 5.5–6.5 mm long. Fruits star-shaped, follicle, spreading, 6–7 mm long. Flowering in October to November.

This new species is categorized in sect. Sedum because it has adaxially gibbous carpels ( Fu & Ohba 2001) ( Fig. 3 ).

Etymology: —The epithet refers to the Japanese name of type locality of the Danjo Islands.

Distribution and habitat: —Endemic to the Danjo Islands (Kyusyu), on sunny, coastal rocky slopes exposed to direct sunlight; in typical coastal vegetation within “a community of Miscanthus condensatus Hackel (1899: 639) – Crepidiastrum lanceolatum (Houtt.) Nakai (1920: 150) ” similar to those in other regions of Japan, Taiwan and the Philippines. Itow & Nakanishi (1990) mentioned that this species was distributed throughout the Danjo Islands (as S. formosanum ), and thus further field surveys are required on the islands.

Additional specimens examined (paratypes): — JAPAN. The Kyushus, the Danjo Islands: Meshima Island, Masao Ejima 15108 (TNS)

IUCN Red list category: —According to the IUCN red list categories criteria ( IUCN 2016), this species should be considered Vulnerable, because it occurs in small islets in the Danjo Islands. At present, the habitat of this species is relatively stable because the Danjo Islands are protected as a Japanese natural monument. However, islets such as the Danjo Islands are easily influenced by subtle climatic changes and competition with naturalized plant species. In fact, naturalized plant species are known to invade the habitats of native plant species in the Danjo Islands ( Toyama 1980). Therefore it is necessary to maintain the environment of these islands and continue to protect it as a national monument.

Japanese common name: —Danjo-mannen-gusa (nov.).

Figures

FIGURE 3. Sedum danjoense. A. Habitat and habit. B. Inflorescence. C. Adaxial surface. D. Abaxial surface. E. Flower. F. Sepals. G. Carpels. H. Branching. Scale bars are 25 mm for A, 5 mm for B–H [A. Wild individuals in Yorishima island photo by Yoshiro Chichibu in May 1989; B. Cultivated in Nagasaki Subtropical Botanical Garden photo by Kiyotaka Minota in Sep. 2011; C-H. Takuro Ito 3658 in Oct. 2016]