Placentation patterns and seed number in fruits of South American Solanum subgen. Leptostemonum (Solanaceae) species

Darwiniana 01/2007; 45(2).
Source: DOAJ


Thirty-seven South American species representing seven sections of Solanum subgen. Leptostemonum were analyzed. Andromonoecious as well as hermaphrodite species were considered. The length and width of their fruits was measured, and the number of seeds per fruit was counted. Medial cross sections of fresh, ripe fruits were observed with a stereoscopic microscope and illustrated. Six placentation patterns and three types of seeds were described. A relationship among seed number, fruit size, fruit color and sexual system was detected by means of statistical analysis. These results suggest that andromonoecy affects fruit size and placentation patterns, in order to contain a higher number of seeds per fruit.

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    ABSTRACT: The mature fruits of 10 South American species of Solanum sect. Torva were studied. Cross and longitudinal microtome sections, stained with astra blue/basic fuchsin, were made for microscopic examination. All species present an epidermis formed by a unistrate layer of small, isodiametric cells, with dense content and cellulosic walls. Immediately below, a hypodermis is always found, consisting of a well-defined layer of lignified cells with a single calcium oxalate crystal occupying the whole lumen of each cell. This is followed by one layer of cellulosic, isodiametric cells with dense cytoplasm and then several collenchymatous layers, sometimes with sclerified cell walls. The mesocarp comprises two zones histologically differentiated: an external one (formed by regular, vacuolated, medium-sized cells with small intercellular spaces), and an internal one, commonly juicy, and developing proliferations among the seeds. The fruits analyzed are alike, and despite some particularities, they can be classified as berries in the conventional sense. All the traits examined agree with the ornithochorous dispersal syndrome. The homogeneity in fruit traits may be due to shared habit, habitat and sexual system.
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