Environmental effects on the developmental morphology of ruscus hypophyllum l.

Ruscus hypophyllum L. is a West Mediterranean species with a fixed morphological organization in which the developmental unit is a sympodial shoot, with an aerial part bearing the phylloclades, and a short subterranean rhizome with two regenerative buds. The mean number of daughter units produced per sympodial unit is 1.42. In irrigated plants growing outdoors, branch emergence is arrested during the summer; it starts in early autumn and stops again for 1 or 2 mo during early winter. A second and more prolonged period of branch emergence starts in late winter and continues until the end of the spring. This bimodal cycle of branch emergence was unaffected by a reduction from 90 to 40% in the level of incident solar radiation. Flower production is also inhibited during the summer. While branch emergence was enhanced by low temperatures (17/12°C) under controlled conditions, it was inhibited by high temperatures (3 2/2 7° C) under both long (16 h) and short (8 h) days. Plants transferred just before the summer from outdoors to 17/12°C continued to produce aerial branches, instead of entering into the rest period like the plants grown outdoors. It is suggested that the inhibition of growth during the summer is not a true summer dormancy, but an arrested growth condition due to the limiting high temperatures of this season.