Fonctionnement sympodial continu et multiplication végétative chez l’Arum italicum

Abstract

The vegetative and floral development of Arum italicum Mill. displays no resting period under western European climatic conditions. Between two flowering seasons several sympodial units ending with an inflorescence are successively built. The meristem of each new unit is generally initiated in the axil of a sagittate leaf of the preceding unit but it can also grow in a nonaxillary position at the base of the meristem. The leaves of the first unit spend the winter season above the ground. Their petiole sheaths surround all the later sympodial units. On each sympodial unit a number of axillary buds give rise to tunicated bulbils which provide for the asexual multiplication of the species. The ontogeny of the bulbils on the mother plant and their behaviour after they become autonomous are described, as well as those of young plantlets grown from seed germination. In rhizomes, bulbils, and plantlets the shoot apex is in close contact with a subapical region (base plate) built from interlocked leaf or scale bases which are rich in storage products. This base plate will give rise to a new rhizome. Although Arum italicum has a tuberous rhizome with sympodial growth, it has nevertheless some characters of a bulbous plant (base plate and bulbils) but it differs from it by continuous growth and development and the lack of dormancy of the bulbils.