Quantitative morpho-anatomical studies of pistillate and staminate flowers of Cucurbita maxima subsp. andreana (Cucurbitaceae)

Abstract

The flowers of Cucurbita maxima subsp. andreana are solitary. Staminate flowers can be found mainly on proximate portions of the branches while the pistillate are on distal portions. Each staminate flower has five monotecal stamens and ca. 90,000 pollen grains, while each pistillate one presents ca. 300 ovules. The axial nectary is symmetric, occupying an area of ca. 100 mm², positioned on the hypanthium, and supplied by phloem and xylem. The following morphological and anatomical parameters of the nectary were considered in order to compare both flower types: nectary surface; distribution, number and size of the stomata; number and diameter of the starch granules and cellular and nuclear diameter of the cells of nectariferous and non-nectariferous tissues. The non-secreting parenchyma showed the highest nuclear and cellular diameter but the lowest value of the nuclear/cell size relationship. No significant differences were found between the cells of the nectary epidermis and those of the secretory tissue. The nectary showed a higher number of starch granules in bud-stage compared to open flowerstage. This fact would indicates that there is a starch accumulation in the nectary until nectar secretion. The results obtained here allow us to relate morpho-anatomical traits with the nectar secretion pattern and with different aspects of the reproductive biology.