Intraspecific variation of phyllotaxis stability in Anagallis arvensis

Abstract

Qualitative transformations of phyllotaxis in Anagallis arvensis occur typically during the generative phase of development. In the vegetative phase phyllotaxis usually does not change. An exception to this rule is one peculiar population of Anagallis arvensis, belonging to a pink-flowered form carnea, in which phyllotaxis often transforms in both the generative and vegetative phase of development. The presence of a relatively large number of vegetative transitions, virtually absent in two control red-flowered populations of form arvensis, is accompanied also by the higher frequency of generative transitions. This might be a result of a genetically determined instability of shoot apex geometry. It has been proved experimentally that changing conditions of growth affect the transition frequencies and the time lapse from the beginning of either the vegetative or generative phase to the transition (measured in plastochrons). A comparison of two types of transitions shows that divergence changes are less abrupt in vegetative transitions. The differences between the two types also pertain to the vertical spacing of leaves and to the pattern formed by leaf bases and wings on the stem surface in the transition zone.