Abstract
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.
Highlights
Kflower varied widely among the species we studied from a mean of 1.30 mmol s-1 m-2 MPa1 for Cornus florida inflorescences to 18.79 mmol s-1 m-2 MPa-1 for Calycanthus occidentalis flowers (Figure 2a)
The three magnoliid genera spanned most of the variation in Kflower of all species measured, ranging from 2.38 mmol s-1 m-2 MPa-1 for Liriodendron tulipifera to 18.79 mmol s-1 m-2 MPa-1 for Calycanthus occidentalis
Varied from 1.71 mmol s-1 m-2 MPa-1 for Iris douglasiana to 4.03 mmol s-1 m-2 MPa-1 for Agapanthus africanus, while the eudicots ranged from 1.30 mmol s-1 m-2 MPa-1 for Cornus florida inflorescences to 3.81 mmol s-1 m-2 MPa-1 for Paeonia suffruticosa
Summary
Plant materialWe collected flowering shoots from around the University of California, Berkeley, campus and from the University of California Botanic Garden during the springs of 2013 and 2014, and from the Marsh Botanical Garden, New Haven, CT, in the spring of 2015. We chose a phylogenetically diverse set of species that varied by almost two orders of magnitude in floral display size (Table 1). These species varied morphologically, from flowers with undifferentiated perianths to those with a fully differentiated calyx and corolla and from those with free petals to those with sympetalous connation. We included inflorescences of Cornus florida (Cornaceae), which have small, inconspicuous flowers but large, white bracts as their showy organs. The showy floral structures of this set of species are not homologous, they have a convergent function of attracting pollinators.
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