Chromosome Science 18: 3-8, 2015 Nure Ferdousee et al. 3

Regular Article

Karyological observations on dwarf individuals of brevicornuta Hayata () growing in the riparian habitat in Amami-Oshima of the Ryukyus, Japan

Nure Ferdousee, Tetsuo Denda and Masatsugu Yokota

Received: April 20, 2015 / Accepted: June 06, 2015 © 2015 by the Society of Chromosome Research

Abstract Introduction Cytotaxonomical studies were conducted on Pilea Pilea brevicornuta Hayata (Urticaceae), a perennial herb brevicornuta Hayata in the Ryukyu Islands and Taiwan. that is very common on the moist forest floor of the Ryukyu Karyomorphology of dwarf and creeping individuals Islands (the Ryukyus) (Walker 1976), is known for its growing in riparian habitat of Amami-Oshima Island, highly variable size (Hatusima 1959). Recently, dwarf which is morphologically distinct from normal individu- individuals of P. brevicornuta with creeping habit have als growing in forest floor, is the main focus of this re- been found by the authors in riparian habitats of Amami- port. All of the studied individuals of P. brevicornuta in- Oshima Island, which are thought to be a rheophytic cluding dwarf ones had same chromosome number of adaptation to river currents. The dwarf and creeping P. 2n = 24. The karyotype formula is 2n = 24 = 6m + 13sm + brevicornuta is clearly distinguished from normal forest 5st for normal individual and 2n = 24 = 6m + 12sm + 6st floor by its miniaturized plant size, nearly obtuse for dwarf individual. The chromosomes of P. brevicornuta apex, less number of serration and high leaf hair density, were all small with sizes varying between 0.9 and 3.0 µm. although taxonomic status of this dwarf and creeping P. Considering the basic chromosome number in the brevicornuta is not clear at present. Pilea, 2n = 24 is regarded as diploid based on x = 12. Intraspecific variations in the chromosome number Despite the high variability in morphology, P. brevicornu- including polyploidy and aneuploidy have been commonly ta had remarkably uniform karyomorphology. found in Urticaceae. Another Urticaceae suzukii Yamaz. shows two aneuploid and three autopolyploid cytotypes (2n = 16, 26, 38, 39, 52) Keywords: Amami-Oshima, chromosome number, Pilea in Yambaru, a northern forested region on Okinawajima brevicornuta, the Ryukyu Islands, Urticaceae. Island of the Ryukyus (Yamashiro et al. 2000). In the case of E. suzukii, the five cytotypes could not be distinguished using morphological characters. Intraspecific polyploidy was also observed in three species; that is, Pe. minima Makino (2n = 26, 39, 52, 65), Pe. radicans (Siebold and Zucc.) Wedd. (2n = 39, 52, 65) and Pe. scabra Benth. (2n = 26, 39, 52, 65) (Kanemoto and Naruhashi 2003). In the case of Pe. minima and Pe. scabra, both of which are morphologically variable species, differences in ploidy level may have some relationships with morphological characteristics (Kanemoto and Naruhashi 2003). These results make us to expect a possibility that there might be some chromosomal variations in association with the morphological differentiation between the normal and dwarf riparian individuals of P. brevicornuta. Cytological observations of some individuals from riparian habitat of Sumiyo River in Amami-Oshima Island have been carried out (Ferdousee et al. 2012). In the previous paper, dwarf Nure Ferdousee ( ) * individuals from single locality were used for cytological Graduate School of Engineering and Science, University of the observation. To deepen our understanding about the Ryukyus, Okinawa 903-0213, Japan cytological features of dwarf form, much more samples E-mail: nure3