Description from Flora of China
Trees deciduous. Leaves alternate; stipule caducous; leaf blade base usually slightly oblique, cordate, truncate, or rounded, margin usually serrate or sometimes entire, often with hairy domatia in axils of veins. Inflorescences axillary, cymose, 3- to many-flowered. Bracts adnate to inflorescence peduncle, band-shaped, large, persistent. Flowers bisexual. Sepals 5, with adaxial nectary at base. Petals 5, white or yellow, imbricate. Stamens many, free or connate into 5 fascicles; anthers 2-locular, dorsifixed; staminodes when present petaloid, tightly enclosing style and stigma, alternating with petals. Ovary 5-loculed, ovoid, usually hairy after anthesis; ovules 2 per locule; style glabrous; stigma apparent, 5-lobed. Fruit a nut or capsule, globose, obovoid, ellipsoid, or ovoid, pericarp usually hairy, mostly woody or fragile and indehiscent, rarely leathery and dehiscent when dry. Seeds 1 or 2.
Tilia is very distinct by its unique bracts adnate to the peduncle of the inflorescence. It is in the process of being monographed by C. D. Pigot, who has studied many populations in China, but this work is not yet available. An initial publication (Pigott, Edinburgh J. Bot. 59: 239-246. 2002) indicated that he intends to accept only 23 species in total, 13 of these occurring in China, and he intends to include many of the more recently described Chinese species within the very variable Tilia tuan. Chromosome numbers were given for all those taxa that he accepts. Tang and Zhuge (Acta Phytotax. Sin. 34: 254-264. 1996) recognized 14 "good" species in China, 17 in E Asia, and 25 in total, but Tang noted that more study for a taxonomic revision is needed.
Modern molecular analyses indicate that Tilia and Craigia form a very distinct lineage that could be treated as a distinct family or subfamily restricted to just these two genera plus the poorly known Central American genus Mortoniodendron Standley & Steyermark.
Between 23 and 40 species: primarily in temperate and subtropical regions; 19 species (15 endemic) in China.