An architectural analysis of Shepherdia canadensis and Shepherdia argentea (Elaeagnaceae): the architectural models

Abstract

The growth patterns of Shepherdia canadensis and S. argentea from seedling stage to adult thicket have been analyzed and compared. In S. canadensis, the seedling axis, originally erect, showed a tendency for early bending towards the horizontal, followed by vertical reorientation of the tip. This was coupled with the basitonic expansion of lateral buds. In contrast, the seedling axis of S. argentea remained erect and branching was predominately acrotonic. As plants of S. canadensis matured, successive branches repeated the seedling pattern, reorienting downward with the tip compensating to remain erect. Basal buds expanded to fill the gap in the canopy and these in turn reoriented downward, repeating the cycle and forming a thicket with the youngest shoots in the centre. Rooting of the horizontal axes was observed and in some cases new thickets could be inititated in this way. In S. argentea, however, shoots remained erect and thicket formation occurred by the expansion of ramets from root buds at the periphery of the thicket. The shoots at the centre were thus the oldest. These features, together with information on branching patterns previously reported, have been used to construct constrasting architectural models for the two species. Key words: Elaeagnaceae, Shepherdia, Buffaloberry, architecture, morphology, development.