Gynoecial morphology and funicular germination plugs in the Nolanaceae



In Nolana humifusa (Gouan) Johnst. and N. paradoxa Lindl, five carpel primordia unite by their thin margins to form the gynoecium wall. An ovule primordium is initiated in each of a maximum of six depressions, formed in the adaxial surface of each carpel primordium. The depressions become deeper, each developing into a duct that ends in an ovule chamber, which is a uniovulate locellus. The locellus is delimited by a ventral carpellary epidermis except at its lower adaxial part, where the ovule is invaginated on a short funicle from its own placenta.

Periclinal cell divisions in the subsurface layers of the floral apex form a receptacular column, which grows in continuity with the lower adaxial parts of the carpel primordia; the upper parts of the carpel primordia face the five-radiate “common cavity” inside the gynoecium wall. At anthesis this cavity is filled with stylar and ovarian transmitting tissue. The latter forms five “wings” that downward are continuous with wings of the receptacular column and which together with them radiate between the five carpels. True septa are not formed.

In N. humifusa a plurilocellate mericarp originates from each carpel primordium. In N. paradoxa longitudinal unilocellate portions of each plurilocellate carpel primordium develop independently into “carpel-lobes”, the bulging lower parts of which mature into unilocellate mericarps. In both species the funicle develops into a germination plug.

The locellar organization described is a common feature of the Nolanaceae. The formation of invariably uniovulate placentae in pluriovulate carpels is the basic innovation of the family.