Fifteen species of Fagaceae from Chiang Mai province, northern Thailand, were investigated: eight Castanopsis, four Lithocarpus and three Quercus species. The species were generally diploid with the chromosome number 2n = 24, and the basic number x =12 was confirmed in some species with meiosis. One tree belonging to Q. lenticellatus had 2n = 14. Chromosomal mapping of the highly repetitive 18S-25S and 5S ribosomal genes by fluorescence in situ hybridisation (FISH) was performed. Most species (from all three genera) showed four 18S-25S rDNA sites (two pairs: one subterminal major and one paracentromeric/intercalary minor loci) and two 5S rDNA sites (one pair: paracentromeric locus). Quercus kerrii also had two pairs of 18S-25S rDNA sites, but both were subterminal major loci. Two species, C. argentea and Q. brandisianus, only had one pair of 18S-25S rDNA sites. Two species, C. calathiformis and L. vestitus, showed an odd number of (unpaired) sites, and this indicated hybrid origin and/or polyploidy. Polyploid cells were detected in these species. The ribosomal gene maps based on both sequences together were genus-specific. In Castanopsis, the 18S-25S and the 5S genes were localized on three different chromosome pairs, and comprised species-specific maps. On the other hand, the ribosomal genes in Lithocarpus and Quercus were found only on two chromosome pairs, because one of the two 18S-25S rDNA loci was localized on the same chromosome as the 5S rDNA locus. The FISH markers may be used to clarify discrepancies arising from morphological assessments.

Basil, Ocimum L., is an economically important member of the family Lamiaceae. It has been widely used for many purposes, such as culinary herbs. The genus harbors large variation in chromosome number and size, which is believed to be a consequence of centuries of cultivation and selection for desirable traits. Meiosis was examined in five Ocimum species from Thailand, from five populations of each species. The results revealed that three of these species are cytogenetically related, forming a polyploid series with a base chromosome number of x=13: O. americanum L. (2n=2x=26, a new number for Thai plants), O. basilicum L. (2n=4x=52) and O. africanum Lour. (2n=6x=78, a new number for the genus). Two species with small chromosomes, O. tenuiflorum L. (2n=36) and O. gratissimum L. (2n=40), seem probably tetraploids with base numbers x=9 and 10, respectively. Meiotic irregularities in O. basilicum and O. africanum suggested that the species may be newly formed polyploids undergoing diploidization. Unlike recent polyploids, the meiotic chromosomes of O. tenuiflorum and O. gratissimum are entirely stable. Statistically significant intraspecific variation in chiasma frequencies was found in O. basilicum and O. africanum and the variation appeared to be geographically associated. The results presented here are useful both in the conservation of native basil species and in the breeding of elite accessions.