# Morphological and Transcriptome Analysis of the Near-Threatened Orchid Habenaria radiata with Petals Shaped Like a Flying White Bird

## TL;DR

This study explores how the unique bird-shaped lip of the Habenaria radiata orchid forms, combining morphological observations and gene expression analysis.

## Contribution

The study reveals the cellular and genetic mechanisms behind the formation of the bird-shaped lip in Habenaria radiata.

## Key findings

- The wing part of the lip folds inward in the bud and expands rapidly after blooming.
- Serrations form initially through cell division and later through polar cell elongation.
- Genes related to floral organ development and serration formation are expressed in floral buds.

## Abstract

Orchids have evolved flowers with unique morphologies through coevolution with pollinators, such as insects. Among the floral organs, the lip (labellum), one of the three petals, exhibits a distinctive shape and plays a crucial role in attracting pollinators and facilitating pollination in many orchids. The lip of the terrestrial orchid Habenaria radiata is shaped like a flying white bird and is believed to attract and provide a platform for nectar-feeding pollinators, such as hawk moths. To elucidate the mechanism of lip morphogenesis, we conducted time-lapse imaging of blooming flowers to observe the extension process of the lip and analyzed the cellular morphology during the generation of serrations. We found that the wing part of the lip folds inward in the bud and fully expands in two hours after blooming. The serrations of the lip were initially formed through cell division and later deepened through polar cell elongation. Transcriptome analysis of floral buds revealed the expression of genes involved in floral organ development, cell division, and meiosis. Additionally, genes involved in serration formation are also expressed in floral buds. This study provides insights into the mechanism underlying the formation of the unique lip morphology in Habenaria radiata.