Floral initiation and development of the sex-changing plant Arisaema sikokianum (Araceae)

Floral initiation and development in Arisaema sikokianum (Araceae) were investigated by scanning electron microscopy. Arisaema sikokianum has a sympodial shoot with a 2-yr growth cycle. Inflorescence initiation occurred on the apex of the axillary shoot of the lower leaf in May. The apex initiated the spathe and spadix in succession. Floral primordia appeared on the spadix from September to October. Both male and female floral primordia appeared as slight bulges on the spadix surface. In female flowers, the primordia became torus shaped, and the margin grew upward as a gynoecium wall; the opening of the style canal remained narrow, and finally stigma papillae appeared on it. Inside the gynoecium wall, ovule primordia developed at the bottom of the ovary cavity, and intraovarian trichomes appeared at the opposite side of ovule primordia. Trichomes played an important role in fertilization. In male flowers, the top of the primordia divided into two or four parts and developed into sessile anthers.