# The water-related traits of flowers are more conservative than those of leaves for epiphytic and terrestrial species in Cymbidium, Orchidaceae

## TL;DR

Epiphytic orchids have leaves adapted to conserve water, but their flowers show no such adaptations, suggesting flowers and leaves evolve separately in response to environmental stress.

## Contribution

This study reveals that floral traits in Cymbidium orchids are not influenced by life form, unlike leaf traits, indicating developmental modularity and decoupled evolution.

## Key findings

- Epiphytic Cymbidium species have thicker leaves, heavier leaf mass per area, and slower water loss compared to terrestrial species.
- Floral traits show no significant differences between epiphytic and terrestrial Cymbidium species.
- Floral and leaf traits are not strongly correlated, suggesting they evolve independently.

## Abstract

Epiphytes occupy arboreal niches in forest ecosystems, which are particularly vulnerable to drought stress due to the absence of a buffered substrate for water retention in epiphytic habitats. Characterizing the differences and relationships among plant morphological and physiological traits is critical for elucidating different adaptive strategies. However, it is still unclear whether there are differences in floral and leaf morphological and physiological traits between epiphytic and terrestrial plants, and whether there is a correlation between flower and leaf traits in epiphytes. Here, we measured 13 floral traits and 8 leaf traits from 7 terrestrial and 12 epiphytic Cymbidium species. We found that, compared with these terrestrial Cymbidium species, epiphytic species had a higher leaf mass per unit area, greater leaf thickness, a longer time required to dry saturated leaves to 70% relative water content, and greater epidermal thickness. However, no significant differences in floral traits were found between the epiphytic and the terrestrial species, which suggest that the water-related traits of flowers in Cymbidium are not influenced by the plant's life forms. Moreover, there were no strong associations between floral and leaf morphological and physiological traits floral traits, implying that they may be developmentally modular. These findings provide novel insights into the decoupled evolution of vegetative and reproductive traits in response to environmental pressures. By shedding light on this pattern, our study advances the understanding of plant adaptation strategies in heterogeneous habitats within the genus Cymbidium, providing a more comprehensive view of how plants evolve to flourish in diverse ecological conditions.

Our results showed epiphytic Cymbidium species had thicker, heavier leaves with tougher epidermis and slower water loss, but their flowers showed no differences from terrestrial species. Flower and leaf traits were also unrelated, suggesting they evolve independently. These findings provide insights into the decoupled evolution of vegetative and reproductive traits in response to environmental pressures.