Floral Longevity of Paphiopedilum and Cypripedium Is Associated With Floral Morphology

Abstract

Floral longevity (FL) is an important trait influencing plant reproductive success by affecting the chance of insect pollination. However, it is still unclear which factors affect FL, and whether FL is evolutionarily associated with structural traits. Since construction costs and water loss by transpiration play a role in leaf longevity, we speculated that floral structures may affect the maintenance and loss of water in flowers and, therefore, FL. Here, we investigated the slipper orchid Paphiopedilum and Cypripedium, which are closely related, but strongly differ in their FL. To understand the evolutionary association of floral anatomical traits with FL, we used a phylogenetic independent comparative method to examine the relationships between 30 floral anatomical traits and FL in 18 species of Paphiopedilum and Cypripedium. Compared with Paphiopedilum species, Cypripedium species have lower values for floral traits related to drought tolerance and water retention capacity. Long FL was basically accompanied by the thicker epidermal and endodermal tissues of the floral stem, the thicker adaxial and abaxial epidermis of the flower, and low floral vein and stomatal densities. Vein density of the dorsal sepals and synsepals was negatively correlated with stomatal density. Our results supported the hypothesis that there was a correlation between FL and floral anatomical traits in slipper orchids. The ability to retain water in the flowers was associated with FL. These findings provide a new insight into the evolutionary association of floral traits with transpirational water loss for orchids under natural selection.

Linkages between stomatal density and minor leaf vein density across different altitudes and growth forms

“…In fact, water supply and demand in leaves are primarily determined by minor leaf vein density (VLA) and stomatal density (SD), respectively ( Brodribb et al., 2017 ). Currently, many studies have observed a positive relationship between SD and VLA ( Carins Murphy et al., 2014 ; Brodribb et al., 2017 ; Lei et al., 2018 ), but negative or marginal correlation is also found in some cases ( Zhang et al., 2015 ; Zhang et al., 2021 ). Thus, there is still controversy over the direction of SD-VLA coordination and whether such coordination is a common feature.…”

Genome Size and Labellum Epidermal Cell Size Are Evolutionarily Correlated With Floral Longevity in Paphiopedilum Species

“…Floral longevity is the length of duration that flowers remain open and functional, which is a key floral characteristic that impacts the reproductive fitness of plants (Primack, 1985 ). Floral longevity varies considerably from a day or less (e.g., Ipomoea purpurea ) up to 2 months (e.g., some species from Orchidaceae ) among flowering plants (Kerner von Marilaum, 1895 ; Gori, 1983 ; Primack, 1985 ; Ashman and Schoen, 1994 ; Zhang et al, 2017 , 2021 ). Some studies have indicated that the duration of the life history in leaves was correlated with genome size within vascular plants (Finch, 1990 ; Morgan and Westoby, 2005 ; Beaulieu et al, 2007 , 2008 ; Théroux-Rancourt et al, 2021 ).…”

“…However, a previous study found a weak positive correlation between leaf lifespan, leaf mass per area, and genome size, suggesting that among angiosperms, genome size and leaf strategy are not related (Morgan and Westoby, 2005 ). Variation of floral longevity may imply different ecological strategies (Zhang et al, 2021 ). Therefore, understanding the genetic basis of variation in floral longevity is of great value.…”

“…The family Orchidaceae is an important group of flowering plants with great values in ornamental, medical, conservation, and evolutionary research (Zhang et al, 2018 ). The high diversity in morphology, floral longevity, growth form, habitat, and genome size mean that orchid species exhibit various biological and ecological consequences (Cox et al, 1998 ; Chase, 2005 ; Leitch et al, 2009 ; Zhang et al, 2017 , 2018 , 2021 ). The genus Paphiopedilum species are commonly named as “Lady's or Venus's Slipper” orchids, and these species are among the most cultivated and horticulturally important plants (Liu et al, 2009 ; Parveen et al, 2012 ).…”

“…Their flowers have long life span, and they can remain on the plant for 62 days (Zhang et al, 2017 ). However, there are few studies on factors influencing floral longevity of Paphiopedilum species (Zhang et al, 2017 , 2021 ). In this study, we examined the potential link between floral longevity, sizes of genomes, and cells in 13 Paphiopedilum species.…”