Table of Contents
ISRN Ecology
Volume 2013 (2013), Article ID 476862, 6 pages
http://dx.doi.org/10.1155/2013/476862
Research Article

Dominant Occurrence of Cleistogamous Flowers of Lamium amplexicaule in relation to the Nearby Presence of an Alien Congener L. purpureum (Lamiaceae)

1Laboratory of Insect Ecology, Graduate School of Agriculture, Kyoto University, Kitashirakawa, Kyoto 606-8502, Japan
2Center for Ecological Research, Kyoto University, Shiga, Otsu 520-2113, Japan
3Osaka City Institute of Public Health and Environmental Sciences, 8-34 Tojo-cho, Tennoji-ku, Osaka 543-0026, Japan
4The Nagoya University Museum, Furo-cho, Nagoya 464-8601, Japan
5Department of Ecosystem Studies, School of Environmental Science, The University of Shiga Prefecture, Hikone 522-8533, Japan

Received 21 March 2013; Accepted 15 April 2013

Academic Editors: P. Ferrandis and P. Rey

Copyright © 2013 Yasuhiro Sato et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Here we document a novel phenomenon that, based on field observations in central Japan, cleistogamous flowers (or closed flowers) of an annual herb Lamium amplexicaule were dominantly expressed near an alien congener L. purpureum. The proportion of cleistogamous flowers in an individual L. amplexicaule increased with the frequency of L. purpureum occurring in the same patches but did not increase with the total density of Lamium plants and their own size. To confirm the consistency of the effect of the coexisting alien species, we assessed the cleistogamous frequency at the patch level for three other populations. In these populations as well, the proportion of L. amplexicaule producing cleistogamous flowers increased with the frequency of L. purpureum. Our transplant experiment at one site found no effect of the nearby presence of L. purpureum on the seed set of L. amplexicaule and therefore did not support the hypothesis that the adverse effect on the reproduction via interspecific pollination favored cleistogamous flowers that accepted no external pollen. Further studies must be conducted to examine the negative interactions between the related species before and after seed development.