Trapa incisa Siebold & Zuccarini var. pubescens Z. F. Yin, L. Y. Sun & Z. Jiang, 2019

Sun, Li-Yong, Jiang, Zheng, Ding, Yu-Long & Yin, Zeng-Fang, 2019, A new variety of Trapa incisa (Lythraceae) from Lake Tai, China, Phytotaxa 397 (1), pp. 121-124 : 121-123

Trapa incisa Siebold & Zuccarini var. pubescens Z. F. Yin, L. Y. Sun & Z. Jiang , var. nov. ( Fig. 1 )

Type:— CHINA. Jiangsu: Suzhou City, Xiangcheng District, coastal waters of northeastern Lake Tai, 31° 23.827′ N, 120° 23.843′ E, 1 August 2018, Li-Yong Sun & Zeng-Fang Yin 080101 (holotype NF!, isotype NF!).

Diagnosis:— Trapa incisa var. pubescens is highly similar to Trapa incisa var. incisa and Trapa incisa var. quadricaudata Glück (1929: 605) in phenotype, but can be distinguished by its pubescent pedicels (versus glabrous in the other varieties), pubescent hypanthia (vs. glabrous) and pink petals 10–12 mm long (vs. white petals 5–7 mm long) ( Table 1).

Description:—Herbs annual, aquatic, rooted or floating. Roots dimorphic; absorbing roots wire-like, growing in sediments; adventitious roots pinnately dissected, greenish brown, anabolic. Stem submerged, slender, branched, upper internodes shortening, 1–2.5 mm in diam. Leaves dimorphic. Floating leaves alternate, crowned into a rosette on upper part of stems or branches; leaf blades approximately rhombic, 2–3 cm × 2–3 cm, adaxially dark green and glabrous, abaxially green and sparsely pubescent, with plenty of brown spots among veins, middle-upper margins irregularly-sharply serrate and lower part entire, base broadly cuneate; petiole 3–10 cm, green, middle-upper part inflated and sparsely pubescent, lower part glabrous. Submerged leaves alternate, small, caducous. Flowers bisexual, solitary in leaf axils, flowering at water surface. Pedicel slender, only upper part pilose when it’s young and then decreasing to be sparsely pubescent. Hypanthium deeply 4-lobed, green and sparsely pubescent; sepals 4, one pair glabrous and apex fuchsia, another pilose along ridge and green. Petals 4, pink, obovate, apically emarginate, 10–12 mm long. Stamens 4, antesepalous; filaments filiform; anther introrse, versatile, dorsifixed, higher than stigma. Ovary subinferior, 2-locular; ovules anatropous, pendulous, 1 per locule; style slender, stigma capitate. Flower disk equally 8-plicated, nearly smooth, with several papillate glands. Fruit narrowly rhombic, ca. 1.5 cm × 1.5 cm × 1 cm, 4-horned, acute, subulate, unequal, 2 upper horns horizontal to ascending, ca. 10 mm, 2 lower horns descending, ca. 5 mm, apex barbellate; fruit apex topped by a conic beak, ca. 3 mm, crest absent. Carpopodium slender, 1.5–2 cm. Seed 1; cotyledons unequal, 1 large, starchy, retained in fruit, 1 small, scale-like, germinating from fruit apex; endosperm absent. Flowering July–August, fruiting August–October.

Etymology:—From the Latin vocabulary pūbēscō, present participle, referring the pubescent pedicels of this new variety.

Geographical distribution:— Trapa incisa var. pubescens is only known in northeastern Lake Tai, Jiangsu Province. In spite of intensive sampling that we carried out during our fieldwork in 2018, no more occurrence of this variety was found in other waters except the type locality.

Conservation status:— Trapa incisa var. pubescens is only known from the type locality in coastal waters of northeastern Lake Tai, Jiangsu Province. Only one population has been found so far. Seriously, it is being disturbed by human activities and no effective protection has been done. Based on its current distribution status and rather small population size, it clearly should be classified as CR (Critically Endangered) according to IUCN Red List Criteria (IUCN 2017).

Paratypes:— CHINA. Jiangsu: Suzhou City, Xiangcheng District, coastal waters of northeastern Lake Tai , 31° 23.827′ N, 120° 23.843′ E, 1 August 2018, Li-Yong Sun & Zeng-Fang Yin 080102 ( NF!) ; idem, 1 August 2018, Li-Yong Sun & Zeng-Fang Yin 080103 ( NF!) .

Figures

FIGURE 1. Trapa incisa var. pubescens (from the holotype).—A. Habitat.—B. The entire plant.—C. Adaxial and abaxial views of leaf.—D. Flower bud and flower.—E. Various parts of a flower, including calyxes, petals, pistil and stamens.—F. Longitudinal section of ovary (up) and floral disk (down).—G. Fruits in different developmental stages.