Researchers reveal how new species treated as colour variant in plants
Washington, US: Once upon a time, photosynthesis and green leaves were thought to be fundamental aspects of plants. Some plants, however, no longer use photosynthesis and now obtain their nourishment from other living things.
One such mycoheterotrophic plant is the ubiquitous Monotropastrum humile, which has a ghostly appearance and is distributed throughout East and Southeast Asia. It frequently flourishes in shaded woodlands where it feeds on the hyphae of fungi to get the nutrients it requires. It was once thought that there was just one species of this plant in the world, despite its widespread distribution. However, a variation found in Japan has been revealed by Professor SUETSUGU Kenji and colleagues to be a brand-new species, upending our knowledge of this peculiar-appearing genus of plants.
It has rosy pink petals and stems resembling milk glass, giving it a beautiful, otherworldly appearance. As it was first found around Kirishima in Kagoshima Prefecture, Japan, the new species has been named Monotropastrum kirishimense.
Originally, this new species was tentatively treated as a color variant of M. humile, known as M. humile f. roseum. Thus began an extensive and multifaceted 20-year study to determine how exactly these plants differed. Specimens were collected from Japan and Taiwan, as well as Vietnam.
Results of various analyses revealed morphological differences (Figures 1-3), including the following; M. kirishimense flowers and ovaries are more rounded than those of M. humile, and its rootball is more obscured by the surrounding soil (in contrast to M. humile's protruding root tips). M. kirishimense individuals are shorter above ground (under 5cm) and longer below ground (over 10cm).
The flowering season is different too; M. humile flowers bloom approximately 40 days earlier than M. kirishimense. As the two plant species have the same primary pollinator (the bumblebee Bombus diversus), this difference in flowering times can reduce heterospecific pollen deposition, helping to ensure conspecific mating, and thereby preventing them from producing hybrids.
There are several other possible reasons why M. kirishimense and M. humile may have evolved into separate species. One possibility is that they have become specialized in feeding on different fungi, which has led to reproductive isolation, or the inability to produce offspring together.
This process is known as resource partitioning and is one of the major ways that species can evolve from a common ancestor. Genetic analysis of mycobionts revealed that M. kirishimense has a consistent, specialized association with a particular lineage of fungi, whereas M. humile is associated with different lineages (Figure 4).
This study suggests that M. kirishimense may have evolved into a new species by relying on a specific type of fungus. In fact, the phylogenetic tree (a 'family tree' of the evolutionary history of a group of organisms) of the plants themselves shows that the genetic characteristics of M kirishimense and M humile can be separated into two clades (Figure 5).
Based on the researchers' analysis of various characteristics, it has been revealed that M. kirishimense is distinct from M. humile in terms of its appearance, flowering patterns, evolutionary history, and ecological relationships. The researchers concluded that it should be recognised as an independent species.
