Chromosome Homology in the Ceratobium, Phalaenanthe, 
and Latourea Sections of the Genus Dendrobium 1 
H. Kamemoto, K. Shindo, and K. Kosaki 
The Dendrobium genus comprises over 1,000 
species of epiphytic orchids distributed over a 
vast triangular area connecting India, New Zea- 
land, and Japan, and including most of the 
tropical and subtropical land areas between 60 
and 180 east longitude. This large genus has 
been subdivided into numerous sections on the 
basis of morphological characteristics ( Holttum, 
1957). Members of the Ceratobium, Phalae- 
nanthe, and Latourea sections are distributed in 
New Guinea and surrounding areas. Both Cera- 
tobium and Latourea are represented by at least 
30 species each, while Phalaenanthe includes a 
relatively few species. Several species in these 
sections have been widely cultivated and exten- 
sively hybridized to produce the improved and 
popular horticultural varieties of today. 
Cytological investigations to date have re- 
vealed 2n = 38 for all species in Ceratobium, 
Phalaenanthe, and Latourea sections, and both 
2n = 38 and 40 in other sections but with 38 
predominating (Ito and Mutsuura, 1957; Ko- 
saki, 1958; Vajrabhaya and Randolph, 1961; 
Kosaki and Kamemoto, 1962). Thus divergence 
of species in the genus appears to have been 
accompanied by little or no change in chromo- 
some number. 
During the past 2 decades, numerous intra- 
and intersectional species hybrids in Dendro- 
bium have been produced by various orchid 
hybridizers. Since cytological studies, particularly 
observations on chromosome homology, are very 
useful in elucidating taxonomic and phyloge- 
netic relationships, as well as in aiding the 
breeding of orchids, the present investigation 
was initiated to examine the meiotic behavior 
of all available species and hybrids involving the 
Ceratobium, Phalaenanthe, and Latourea sec- 
1 Published with the approval of the Director of 
the Hawaii Agricultural Experiment Station as Tech- 
nical Paper No. 6 14. This study was supported by the 
National Science Foundation (G-13582). Manuscript 
received March 22, 1963. 
tions, and to establish the relationships of spe- 
cies of these groups. 
MATERIALS AND METHODS 
The species involved in this study are listed 
in Table 1 along with their geographical distri- 
bution, while the hybrids with their registered 
names are found in Table 2. Plants were ob- 
tained from the Foster Botanical Garden and 
orchid nurseries in Honolulu. Young pollinia 
were sliced and fixed in 1:1 : 2 mixture of chloro- 
form, 95% ethyl alcohol, and glacial acetic acid 
for 20-30 min at room temperature. They were I 
then transferred to 45% acetic acid for 20-30 1 
min to soften the tissue and promote the 
stainability of chromosomes. They were then 
squashed and stained in 1% aceto-orcein. 
OBSERVATIONS 
Meiosis in Species 
Meiosis in 11 species representing the sec- 
tions, Ceratobium, Phalaenanthe, and Latourea 
(Figs. 1-12) showed consistently 19 bivalent 
chromosomes at metaphase I (Table 3). The 
products of meiosis were normal tetrads with 
19 chromosomes distributed in each microspore. 
The bivalents were either rod or ring shape 
with terminalized chiasmata (Figs. 24-26). The 
size of bivalents differed markedly within a 
complement. This difference was more conspicu- 
ous in species of Ceratobium and Phalaenanthe 
than in Latourea. There were also distinguishable 
differences in the genomes of different species 
within the same section. 
Metaphase I configurations of D. undulatum 
were characterized by the presence of conspicu- 
ously large and heteropycnotic bivalent chromo- 
somes (Fig. 24) which were readily discernible 
at late prophase and metaphase of either meiosis 
or microspore division. These chromosomes 
104 
