Life-history monographs of Japanese plants. 5: Trillium tschonoskii Maxim. (Trilliaceae)

Life-history characteristics and demography of Trillium tschonoskii (Trilliaceae) were studied and are described here. Trillium tschonoskii is the most wide-ranging species among Asiatic Trillium, ranging from southern Sakhalin, the Japanese Islands (excepting Kyushu) to the Korean Peninsula, Taiwan and further to inland China and the Himalayas. The ecological range of T. tschonoskii is broad, extending from lowland forests to montane and further to subalpine mixed forests consisting of conifers and subalpine birch, Betula ermani. This species is a typical polycarpic perennial, similar to all other Japanese Trillium species, and flowers in early to late April in lowland populations and in mid-June to early July in subalpine habitats. Trillium tschonoskii typically has three white petals and three sepals, and its pollinators are diverse, for example, flies, beetles and bees such as Scatophagiae (Diptera), Oedemera lucidicollis (Coleoptera) and Andrena sp. (Hymenoptera). Pollen[solidus]ovule ratios of T. tschonoskii are approximately 700, thus T. tschonoskii is potentially an inbreeder. Seed outputs per plant are variable, 29-190 (mean 85.0) in 1980, and 28-168 (mean 79.8) in 1984. Seeds with a large soft juicy elaiosome attract ants, which are effective dispersal agents, but nocturnal elaiosome predators, mainly ground beetles, are also very active. Our long-term observations indicate that it takes approximately 10 years to reach a sexually mature stage and the life expectancy of mature plants is assumed to be exceedingly long, extending over 40 years.