The genus Hemiboea is a curious genus of the tribe Didymocarpeae (Cyrtandroi-
deae), characterized by its peculiar pistil with one fertile carpel and its follicle-like capsule. This genus has not yet been thoroughly studied since its establishment by C. B. Clarke in 1888. In
the present paper, the taxonomic history is briefly reviewed; the external morphology, leaf his-
tology, pollen morphology and geographical distribution are discussed; a key to the 21 species
recognized by the author is provided; and the economic uses reported in various publications
are summarized.
I. Morphology
(1) Sclereids The foliar sclereids, occurring in this genus and defined by their forms,
fall into two types.
(A) Vermiform selereids This type of sclereids is noted in 15 species and may be clas-
sified into two groups according to their positions in leaf tissues. Those of the first group
are interspersed in the ground tissue around the vascular bundles of leaves and noted in 12
species, i.e.H. longisepala, H. cavaleriei, H. bicornuta, H. fangii, H. omeiensis, H. gracilis,
H. glandulosa, H. mollifolia, H. pingbianensis, H. parviflora, H. strigosa and H. gamosepala,
and those of the second group are dispersed in the mesophyll, occurring in H. subcapitata, H.
henryi and H. latisepala.
(B) Astrosclereids The sclereids of this type are discovered for the first time in Hemiboea,
dispersed in the mesophyll of a single species, i.e.H. lungzhouensis.
No foliar sclereids are found in the remaining 5 species, i.e.H. integra, H. flaccida, H.
longgangensis, H. subacaulis and H. follicularis.
The differences in forms and positions of the foliar sclereids and their absence or pre-
sence are of great help in understanding the relationship between the infrageneric taxa.
(2) Pollen grains The pollen grains of 19 species were examined with LM and SEM.
They are 3-colporate, subglobose or prolate, 20-38.8×22-28μm. The exine is 1.3-2μm
thick and the sculpture is foveolate (e.g.H. cavaleriei) to reticulate (e.g.H. omeiensis). In
Sect. Subcapitatae the pollen grains are subglobose or prolate, while those of Sect. Hemiboea are
prolate.
No pollen grains are observed in anthers of 13 speciemens of H. subacaulis var. subacaulis
and var. jiangxiensis.
(3) Seed-coat Under SEM the seed-coat exhibits considerable diversity in the genus, fur-
nishing useful characters for explaining the relationship between the two sections.
2. Geographical distribution The genus Hemiboea ranges from the eastern border of the
Xizang Plateau and Yunnan Plateau eastwards to Ryu Kyu Islands, and from the southern
slope of the Qinling Range southwards to northern Vietnam. The karst region of S. E. Yun-
nan and W. Guangxi is the centre of maximum variation of the genus and is probably its origin
centre, where the most primitive taxon exists, and where more species (13 species, i.e. 61.9 per
cent of the sum total) and more endemic species (8 species) are found than elsewhere.
3. Classification The genus consists of 21 species and 6 varieties which are classified into
2 sections. The Clarke's classification is accepted, but emended here as follows:
Sect. 1. Subcapitatae Clarke Sepals free or posterior ones connate. Muri of the seed-coat
laevigate or rugose; bottom of meshes flat, smooth or with few verrucae. Pollen grains subglo-
bose or prolate.
Sect. 2. Hemiboea Sepals connate. Muri of the seed-coat tuberculate or aliform-tuberculate;
bottom of meshes flat or concave, with dense verrucae. Pollen grains prolate.
Based on the analysis of external and internal morphological characters, the main evolu-
tionary trends in the genus are discussed and enumerated, and a hypothesis indicating the re-
lationships between the two sections is given.
