The carpology and taxonomic relationships of Davidsonia (Davidsoniaceae)

Abstract

The fruit of Davidsonia pruriens F. v. Muell. drying and splitting at maturity into two indehiscent mericarps is re-defined as a schizocarpic didrupe. The sclerified mesendocarpic construction of the whole pericarp supports its classification as a drupe. The peculiar fimbriate surface of the mericarp is caused by the destruction of parenchymatous exocarpic and mesocarpic tissues exposing radially elongated mesendocarpic osteosclereids. The seed coat is described as diffusive exotegmic with expanding pachychalaza substituting the two integuments in the chalazal half of the seed. The diffusive exotegmy of the spermoderm supports a close relationship with Cunoniaceae, but refutes any relationships with Saxifragales or with Staphyleaceae or any Hamamelidae. The seed-coat structure indicates advancement and specialization of Davidsonia among Cunoniales; its origin could trace back possibly to Rosales, but never to hamamelidalean stock.