Hydraulic conductance and the maintenance of water balance in flowers.

Flowers face desiccating conditions, yet little is known about their ability to transport water. We quantified variability in floral hydraulic conductance (Kflower ) for 20 species from 10 families and related it to traits hypothesized to be associated with liquid and vapour phase water transport. Basal angiosperm flowers had trait values associated with higher water and carbon costs than monocot and eudicot flowers. Kflower was coordinated with water supply (vein length per area, VLA) and loss (minimum epidermal conductance, gmin ) traits among the magnoliids, but was insensitive to variation in these traits among the monocots and eudicots. Phylogenetic independent contrast (PIC) correlations revealed that few traits had undergone coordinated evolution. However, VLA and the desiccation time (Tdes ), the quotient of water content and gmin , had significant trait and PIC correlations. The near absence of stomata from monocot and eudicot flowers may have been critical in minimizing water loss rates among these clades. Early divergent, basal angiosperm flowers maintain higher Kflower because of traits associated with high rates water loss and water supply, while monocot and eudicot flowers employ a more conservative strategy of limiting water loss and may rely on stored water to maintain turgor and delay desiccation.