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Ethereal color variant of mysterious plant is actually a new species

Date:: December 27, 2022
Source:: Kobe University
Summary:: It was thought that there was only one species of the ghost-like Monotropastrum humile plant found in woodlands across East and Southeast Asia. In a major new discovery, botanists reveal that a rosy pink colored variant is actually a distinct new species, shaking up our understanding of this unusual-looking genus of plants. This 20-year study emphasizes the importance of combining various analytical methods to fully understand and protect biodiversity.
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FULL STORY

Green leaves and photosynthesis were once considered essential characteristics of plants. However, some plants have stopped performing photosynthesis and take the nutrients they need from other organisms instead. One such mycoheterotrophic plant is ghostly-lookingMonotropastrum humile在东部和东南部Asi广泛发现a. It often grows in woodlands where there is little sunlight, obtaining the nutrients it needs by feeding off the hyphae of fungi. Despite its wide distribution, it was previously believed that only one species of this plant existed in the world. However, Professor SUETSUGU Kenji and colleagues have discovered that a variant found in Japan is actually a new species, shaking up our understanding of this unusual-looking 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 namedMonotropastrum kirishimense.

Originally, this new species was tentatively treated as a color variant ofM. humile,known asM. humilef.roseum.Thus began an extensive and multifaceted 20-year study to determine how exactly these plants differed. Specimens were collected from throughout Japan and Taiwan, as well as Vietnam.

Results of various analyses revealed morphological differences, including the following;M. kirishimenseflowers and ovaries are more rounded than those ofM. humile,and its rootball is more obscured by the surrounding soil (in contrast to M.humile's protruding root tips). M.kirishimenseindividuals are shorter above ground (under 5cm) and longer below ground (over 10cm). The flowering season is different too;M. humileflowers bloom approximately 40 days earlier thanM. kirishimense. As the two plant species have the same primary pollinator (the bumblebeeBombus 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 whyM. kirishimenseandM. humilemay 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 thatM. kirishimensehas a consistent, specialized association with a particular lineage of fungi, whereasM. humileis associated with different lineages. Therefore, this study suggests that M.kirishimensemay 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 ofM. kirishimenseandM. humilecan be separated into two clades. Based on the researchers' analysis of various characteristics, it has been revealed thatM.kirishimenseis distinct fromM. humilein terms of its appearance, flowering patterns, evolutionary history, and ecological relationships. Therefore, the researchers concluded that it should be recognized as an independent species.

Overall, the research group not only revealed thatM. kirishimenseis a distinct species but also deepened understanding of plants in the Monotropastrum genus. Mycohetrotrophic plants are very vulnerable to extinction as they rely on specific ecosystems to survive and are usually found in old-growth forests. The newly recognized species, M.kirishimense, is rare and presumably endangered. Now that it has been identified as a new species, conservation efforts can be made to protect it. This study emphasizes the importance of combining various analysis methods, called integrative taxonomy, to fully understand and protect biodiversity. This work was conducted by a multi-institutional research group, including Professor Suetsugu (Graduate School of Science, Kobe University), Professor SUYAMA Yoshihisa (Graduate School of Agricultural Science, Tohoku University), and Dr. Tian-Chuan Hsu (Taiwan Forestry Research Institute). The paper was published online inJournal of Plant Researchon November 30, 2022.