Description from Flora of China
Pseudosassafras Lecomte; Yushunia Kamikoti.
Deciduous trees, usually dioecious. Terminal buds large, operculate; bud scales suborbicular, densely sericeous. Leaves alternate, clustered at apex of branchlet, papery, pinninerved or triplinerved, dimorphic, unlobed or 2- or 3-lobed. Raceme terminal, few flowered, lax, pendulous, pedunculate, with late deciduous alternate bracts at base; bracts linear to filiform. Perianth yellow; perianth tube short; perianth lobes 6, in 2 series, subequal, deciduous at side above base. Flowers unisexual or bisexual, pedicellate. Male flowers: fertile stamens 9, inserted on throat of perianth tube, in 3 series, subequal; filaments filiform, longer than anthers, complanate, those of 1st and 2nd whorls eglandular but those of 3rd whorl each with 2 shortly stipitate glands; anthers ovoid-oblong, obtuse but always emarginate at apex, all 4-celled, upper 2 cells smaller, or sometimes anthers of 1st whorl 3-celled (upper cell infertile) or sometimes 2-celled (cells fertile), those of 2nd and 3rd whorls all 2-celled, cells all introrse or lower cells of 3rd whorl lateral, sometimes those of 3rd whorl extrorse; staminodes 3 or absent, if present in innermost whorl, alternate to stamens of 3rd whorl, triangular-subulate, stipitate. Female flowers: staminodes 6, in 2 series, or 12 in 4 series; ovary ovoid, almost estipitate and inserted in short perianth tube; style slender; stigma discoid-dilated. Fruit dark blue, drupaceous, ovoid, with a shallow perianth cup at base; stalk elongate, gradually dilated toward apex, glabrous. Seeds oblong, apiculate, coat thin; embryo subglobose, erect.
Chung, van der Werff and Peng (Observations on the floral morphology of Sassafras randaiense (Lauraceae), Ann. Missouri Bot. Gard., in press) found S. randaiense to have bisexual, protogynous flowers. Recent observations on flowers of S. tzumu (P. H. Raven, pers. comm.) suggest that this species also has bisexual flowers. Chung et al. (loc. cit.) also found that anthers of the 3rd whorl have extrorse rather than introrse cells.
In the phylogeny of the Lauraceae, unisexual flowers appear only three or four times: in Hypodaphnis Stapf, a unispecific genus from W Africa (basal in the family, and with an inferior ovary); in the Litsea group (Actinodaphne, Litsea, Lindera, and Neolitsea, together 400-500 species); in part of Ocotea Aublet and throughout both Rhodostemonodaphne Rohwer & Kubitzki and Endlicheria Nees (together about 300-400 neotropical species); and finally in one species of Sassafras. Sassafras is the only genus with species having unisexual and bisexual flowers. Molecular data indicate that Sassafras is close to the Litsea group but not part of it. One can avoid having species with unisexual and bisexual flowers in Sassafras; the two Chinese species are sister to the North American species (fide Nie et al., Pl. Syst. Evol. 267: 191-203. 2007), and one can split Sassafras into two genera, one with the North American species (with unisexual flowers), the other with the two Chinese species (with bisexual flowers). That would be in agreement with molecular data. One can also not split Sassafras, and that would be supported by molecular data as well.
The two Chinese species differ from the North American one in having perianth puberulent, male flowers each with 3 staminodes and 1 rudimentary pistil, and female flowers each with 12 staminodes.
Three species: disjunctly distributed in China and North America; two species (both endemic) in China.
(Authors: Li Xiwen (李锡文 Li Hsi-wen), Li Jie (李捷); Henk van der Werff)