The rice genus (Oryza L. ) belongs to the grass family(Poaceae) and contains 24
annual or perennial species, including two cultivated rice species, i.e., the Asian rice ( O.
sativa L. ) and African rice (O. glaberrima Steud. ), and 22 wild species distributed
throughout the tropics of the world. Species in this genus have been extensively studied by
scientists with different approaches, including morphological characterization and cytological
and molecular investigations. The leaf epidermis is an important morphological character
which has been studied for taxonomic identification and studies on systematic relationships of
species, particularly in grasses. In this study, morphological features of the leaf epidermis of
23 rice species were observed through light microscopy. The results showed that some char-
acters of the rice leaf epidermis had significant diversity between species and these characters
were valuable for the identifying Oryza species, and for assessing systematic relationships in
the genus. For example, O.schlechteri, O.ridleyi, O.longiglumis, O.granulata,
and O. rneyeriana had elliptic stomatal complexes, whereas the other species had rhombic
stomatal complexes. In most cases, papillae on the surface of the epidermis were variable in
size and distribution between species. The size of papillae varied from small ( 1.5～4.4µm in
diameter), medium-sized (9～18µm), to large (21～30µm) , and the pattern of papillary
size and distribution were very useful for identification of rice species. In addition, the num-
ber and location of the small papillae in stomatal complexes were particularly different be-
tween species. Based on the following combinations of leaf-epidermic characters, i.e., the
size and distribution of papillae on the abaxial surface of the epidermis, the number and loca-
tion of the small papillae in stomatal complexes, and the shape of stomatal complexes, the 23
studied Oryza species could be divided into three major groups. The first group comprises
O.longiglumis, O.ridleyi, O.meyeriana, and O.granulata. In these species, nei-
ther large nor medium-sized papillae, in some cases extremely rare small papillae, were found
on the surfaces of epidermis, and there were no small papillae found in stomatal complexes.
All species in the first group had elliptic stomatal complexes. The second group consists of
O.brachyantha, diploid and tetraploid O.officinalis, O.minuta, O.eichingeri, O.
punctata, O.latifolia, O.alta, O.grandiglumis, O.rhizomatis, and O.aus-
traliensis. In these species usually no large papillae were observed, but medium-sized and
densely populated small papillae were found to cover the surface of epidermis, and at least
four small papillae were found in stomatal complexes (in guard cells) of most species. The
third group contains O.sativa, O.nivara, O.rufipogon, O.longistaminata, O.
glumaepatula, O.meridionalis, O.barthii, O.glaberrima and O. schlechteri. The
abaxial leaf epidermis of these species was usually covered with large papillae, medium-sized,
and small papillae. In addition, more than 4 (usually 6～8 ) small papillae were found in
guard cells or/and subsidiary cells of the stomatal complexes. Most species in the second and
third groups had rhombic stomatal complexes. These results agree mostly with previous re-
ports on the biosystematic studies of rice species by applying other methodologies.
