American Journal of Plant Sciences, 2013, 4, 596-601 http://dx.doi.org/10.4236/ajps.2013.43078 Published Online March 2013 (http://www.scirp.org/journal/ajps) Coastal Adaptation of Adenophora triphylla var. japonica (Campanulaceae) Kyohei Ohga 1 , Miwako Muroi 1 , Hiroshi Hayakawa 2 , Jun Yokoyama 3 , Katsura Ito 2 , Shin-Ichi Tebayashi 2 , Ryo Arakawa 2 , Tatsuya Fukuda 2* 1 Graduate School of Integrated Arts and Sciences, Kochi University, Kochi, Japan; 2 Faculty of Agriculture, Kochi University, Kochi, Japan; 3 Faculty of Science, Yamagata University, Yamagata, Japan. Email: * tfukuda@kochi-u.ac.jp Received January 11 th , 2013; revised February 4 th , 2013; accepted February 18 th , 2013 ABSTRACT The comparative morphology and anatomy of leaves between the coastal ecotype and the normal type of Adenophora triphylla (Thunb.) A.DC. var. japonica (Regel) H.Hara (Campanulaceae) were examined to clarify the differences in morphological characters between the 2 groups. Morphological and anatomical analyses revealed that the coastal eco- type had a thicker leaf than the normal type, because of the increased size of epidermal and spongy cells. Thus, the main morphological change from the normal type into the coastal ecotype of A. triphylla var. japonica is the increase in leaf size, suggesting that the coastal ecotype may have evolved from the normal type via a heterochronic process. Keywords: Adaptation; Adenophora triphylla var. japonica; Coastal; Ecotype; Heterochronic; Leaf Thickness 1. Introduction Plant diversity has fascinated humans throughout history; the diversity is presumably plant adaptation to different natural environments, primarily due to the tremendous variations in morphological traits that exist in nature. The fitness effects of such naturally occurring variation pre- sent within or among species have driven plant evolution by natural selection [1]. In addition, considerable varia- tion exists within many species, which likely reflects adap- tations to different natural environments and is the origin of plant species differentiation [2]. One of the major challenges of plant biology is to de- scribe and understand the morphological mechanisms behind naturally occurring variations for adaptation to various environments. Coastal regions are one type of specific environment that can lead to morphological mo- dification. Plant species growing in coastal regions need to be adapted to an environment in which drought strong- ly affects plant growth [3]. Moreover, water availability is the main environmental factor limiting photosynthesis and growth even in plants well adapted to coastal condi- tions [3]. Another source of stress and an abiotic driver of natural selection in coastal plant communities is soil salinity [4,5]. Different levels of salt spray can result in vegetation zonation; plants adapted to salt spray grow close to the ocean and are replaced by less salt-resistant plants further inland [6,7]. Therefore, plants in coastal regions have developed various interesting morphologi- cal adaptations including succulent tissues to store water, a pubescent epidermis and a thick cuticle to reduce tran- spiration and water loss, belowground structures to with- stand sand burial, and an annual habit [8]. Adenophora triphylla (Thunb.) A.DC. var. japonica (Regel) H.Hara belonged to Campanulaceae is distrib- uted in Japan, Korea, and Sahalin, and includes distinct morphological variations [9] to adapt to various envi- ronments. For instance, the rheophytic ecotype of this variety is found along rivers [10]. This ecotype has a narrower leaf than the non-rheophytic type because of the decreased number and size of the leaf cells [11]. The serpentine ecotype of A. triphylla var. japonica also had narrow leaves, but the leaf thickness and stomatal density was significantly different from those of the normal plants, suggesting that there were different adaptation processes between the two ecotypes of this species [12]. From these studies, it appears that A. triphylla var. ja- ponica can easily alter its morphology and has several ecotypes in various environments. We found the coastal ecotype of A. triphylla var. japonica, which has thick leaves and stems (Figure 1), in some coastal areas of Kochi Prefecture in Japan (Figure 2), where it grows along with other coastal taxa such as Cirsium maritimum Makino (Asteraceae), Dianthus japonicus Thunb. (Ca- ryophyllaceae), Setaria viridis (L.) P.Beauv. var. pachy- * Corresponding author. Copyright © 2013 SciRes. AJPS