STÖCKLIN, J., 1992.Differences in the location of subcotyledonary buds amongEpilobium angustifoliumL.,E. dodonaeiVill. andE. fleischeriHochst. (Onagraceae) and effects on architecture and population structure. Morphological and architectural features in the two closely related pioneer plant speciesEpilobium dodonaeiandE. fleischeriare examined in cultivation and in the field and compared withE. angustifolium.InE. angustifolium, the aerial shoot system is renewed every year from buds on horizontal roots and results in a horizontal spread and a clonal growth form. InE. dodonaei, bud formation is restricted to the hypocotyl and in larger plants to the transitional region between root and shoot. Consequently this species shows no vegetative mobility and develops a shrub‐like habit. The alpineE. fleischericombines the habit ofE. angustifoliumandE. dodonaeiand may either develop successive generations of shoots from the transitional region between root and shoot and/or exploit new areas by horizontal roots and the formation of shoots from root buds. The simple difference in the location of renewal buds is accentuated by cumulative growth. The study shows thatE. dodonaeiandE. fleischeri, which often are considered as subspecies, are separated by fundamental differences in their architectural models. The ecological and demographic implications of these differences are discuss