Fruit and seed micromorphology and its systematic significance in tribe Sorbarieae (Rosaceae)

We investigated fruit and seed morphology in tribe Sorbarieae and one traditionally included genus (Lyonothamnus), which revealed that these characteristics are taxonomically significant for generic delimitation in the tribe Sorbarieae, and two distinct groups in the genus Sorbaria were identified. The following fruit and seed micromorphological characteristics were described: size, shape, texture, the presence/absence of epicuticular wax and, trichomes, testa cell size, and surface ornamentation. Multicellular capitate glands with stalks were only observed on the follicle surfaces of Lyonothamnus. Simple unbranched unicellular non-glandular trichomes were found on the follicles of Chamaebatiaria millefolium, Sorbaria grandiflora, S. sorbifolia complex, and Spiraeanthus schrenkianus. However, Sorbaria arborea complex, S. kirilowii, and S. tomentosa complex had platelet epicuticular wax on their glabrous follicles. Moreover, four types of testa ornamentation were identified: type I, colliculate (Lyonothamnus); type II, reticulate, with straight anticlinal walls and smooth to micro-papillate periclinal walls (Chamaebatiaria); type III, reticulate, with undulate anticlinal walls and smooth periclinal walls (Spiraeanthus); and type IV, reticulate testa ornamentation and divided into two subtypes based on anticlinal and periclinal cell wall patterns (Sorbaria). These studied characteristics identified using principal component analysis may have diagnostic importance among the taxa in the tribe. Our fruit and seed micromorphological results provide strong evidence that genus Lyonothamnus could be positioned in the tribe Lyonothamneae, not Sorbarieae. Moreover, these data supported the preliminary phylogenetic hypothesis that Sorbaria could be divided into two groups.