A morphometric approach to the architecture and ontogeny of the extant sphenopsid Equisetum telmateia Ehrh

Morphometric analyses performed on vegetative shoots of Equisetum telmateia Ehrh. in southern France indicate that the leading axis of the vegetative shoots consists of two growth units. The long nonchlorophyllous portion bears branches and is entirely preformed; the second is represented by a slender chlorophyllous part (with six to eight internodes) that terminates the axis and comprises both preformed and neoformed elements. Lateral branches are slender and chlorophyllous and comprise several neoformed elements. The length of each growth unit is significantly correlated with the capacity for elongation of its internodes (estimated from the length of the longest). The determinate pattern of growth in vegetative shoots is marked by a synchronous decrease of the outer diameter of the main axis, the number of branches, and the number and size of leaves. The initiation of morphogenetic components is presumably adjusted in relation to functional constraints, notably structural support and photosynthesis. Two types of allometric change have been identified in mature vegetative shoots: vegetative stems in long shoots are more slender than short ones and have proportionally more nodes that produce branches. Finally, we hypothesize that fertile shoots consist of only a single preformed growth unit and that the stem portion below the cone is homologous to the proximal part of the preformed portion of the stem in vegetative shoots.