The condition where the shape of a leaf or leaflet is widest for a good length of the leaf along the middle, where both sides of the leaf are roughly parallel for a majority of the leaf blade, such as in Shingle Oak or Blue Beech.
symmetrical form intermediate between a rectangle and ellipse, i.e. with curved ends but sub-parallel sides (e.g. Calciopappus caudatus, Ellipsolithus macellus). N.B. This is recommended botanical use (Stearn 1983).