- A team of Indian and Chinese scientists stumbled across a new species of Didymocarpus, or stoneflower, from northeast India and China.
- Scientists have also rediscovered four species of stoneflowers, and reported India’s first record of a Didymocarpus species previously known only from Bhutan.
- More surveys and explorations into less-studied regions and flora could be spurring this spurt of Didymocarpus discoveries. These gesneriads were also an ignored group of plants previously but more teams are studying these small herbs now, say scientists.
To anyone else, the dried herb pressed neatly into crisp white paper would have been just another herbarium specimen. But for scientists at the Indian Institute for Science Education and Research Bhopal’s TrEE laboratory (Tropical Ecology and Evolution Lab), it was an enigma. From the distinct physical features, doctoral researcher Prasanna N.S. thought it was a stoneflower.
The distinctness lay in several aspects including the creamy-white flowers the half-foot-tall plant bore. The plant in question had been collected by one of Prasanna’s teammates, Preeti Saryan, on her field trip to Nagaland’s Mount Saramati in 2018. Prasanna and Preeti are researchers in the TrEE lab led by associate professor Vinita Gowda.
Prasanna pursued the mystery. It was definitely a Didymocarpus, or stoneflower: the group of plants he was studying for his doctoral research. Digging deeper, he compared the plant’s physical features to those of Didymocarpus specimens preserved in seven herbaria, including those at Kolkata’s Botanical Survey of India and London’s Natural History Museum. He pored over monographs, analyzed digital photographs and online databases. In 2019, his efforts paid off: the plant’s unique morphology confirmed that it was a species new to science.
At the same time, a team from China led by Lei Cai of Yunnan’s Kunming Institute of Botany had also stumbled across the very same species of stone flower from the province of Yunnan. In a unique collaboration, both teams shared their data. They published news of their find – Didymocarpus sinoindicus, named in honour of the teamwork between Indian and Chinese scientists – in a special issue of the journal Rheedea this May.
Stoneflowers and India’s new species
Closely related to the ornamental African violets and Episcias, plants of the genus Didymocarpus – also called “stoneflowers” probably because they often grow on wet rocks and stones – are distributed across south Asia’s wet forests. China is home to 34 species, while India comes a close second with 25, with most of them distributed in the northeastern states. Many are ‘narrow endemics’: species that have very small distributions, and are found nowhere else in the world.
The Indian and Chinese teams’ find of Didymocarpus sinoindicus is the latest in a string of new Didymocarpus species discoveries in India.
Earlier in 2016, scientists from Kerala described Didymocarpus moelleri from Arunachal Pradesh, a species that bursts into flamboyant orange blooms and grows only in one location in the state. A team from the Botanical Survey of India also recorded Didymocarpus bhutanicus, previously know only from Bhutan, for the first time in India (in Sikkim) this February.
These discoveries are thanks to a renewed interest in Didymocarpus in recent times, said Prasanna.
“It used to be rather neglected genus before,” said Prasanna, who is currently studying the phylogeny and biogeography of Didymocarpus for his doctoral research.
The discoveries are also a pan-Asian trend: over the last five years, more than six species of stone flowers have been described from southeast Asia. Cai’s team, for instance, discovered the mauve-blossomed Didymocarpus anningensis from Yunnan in China in 2016 (three years later another team discovered D. brevipedunculatus, a new species of stoneflower that grows on rocky surfaces near seasonal waterfalls, from this very province).
Scientists have also described four other species of Didymocarpus from Cambodia and Vietnam. In 2019, scientists recorded the genus Didymocarpus for the first time in Laos (Didymocarpus middletonii, a new species), followed by the another (Didymocarpus albiflorus, which bears snow-white flowers) this year.
Surveys into previously less-explored areas are definitely helping scientists discover new Didymocarpus species, agrees Cai. Moreover, researchers don’t often spot the plants while they are flowering, he added.
“Someone may have collected it a long time ago, but they didn’t realize that it wasn’t described, just like Didymocarpus sinoindicus,” he wrote in an email to Mongabay-India. “With more careful observation and research, and some luck, maybe researchers can find more beautiful Didymocarpus species.”
The discoveries of new Didymocarpus species is “particularly encouraging” because like many other Gesneriaceae, they are indicators of “intact undisturbed forest ecosystems”, commented Dr. Michael Moeller, scientist at the Royal Botanic Garden Edinburgh who has worked extensively on gesneriads. He did not participate in the study. Surveying and studying previously unexplored or underexplored areas will yield more species new to science, although they might be known locally for many years, he added.
Targeted surveys were in fact what led Gowda and Prasanna to the rediscovery of four Didymocarpus species this year. Timing their field expeditions to catch the plants in bloom between July and September (peak monsoon months), the team forayed into Mizoram and its adjoining areas in 2017 and 2018. They specifically targeted ‘type localities’ or sites from where the first records of Didymocarpus species were made. Their explorations paid off.
One of the four species they rediscovered, Didymocarpus adenocarpus, has been recorded after 87 years. Though the plant was known to be found in southern Mizoram as per its first description in 1928, Gowda and Prasanna did not locate any plants in this area. The population of around 300 individuals that they did spot were restricted to a small 15 square-kilometre area of community forest in northern Mizoram. This would make the species “Endangered” as per criteria listed by the International Union for Conservation of Nature and Natural Resources (IUCN), they write in their study published in Phytokeys.
In their study, the team have also updated and amended the descriptions of these species. The other species rediscovered include Didymocarpus parryorum from south Mizoram which sports small, orange blooms; the mauve-blossomed Didymocarpus lineicapsa from north Mizoram; and Didymocarpus wengeri, which grows on steep clay banks in just two sites in south Mizoram and has been classified as “Critically Endangered” by the team based on the IUCN guidelines (they spotted just 52 individual plants in both locations).
Most of these species were not seen from their type localities but in sites close by suggesting that the plants have been present in the same location for almost 90 years without being recorded in recent explorations, says Gowda. More explorations in the northeast could reveal new species of Didymocarpus, she adds.
Apart from more explorations and thorough documentation, other aspects also need attention according to Gowda.
“Currently, teaching plant taxonomy ends with the description of a plant and no research follows. There’s no focus on the ecology of the species, or research to show the need for its conservation,” she says. “That’s something we hope to focus on in the TrEE Lab at IISER Bhopal.”
A lot of research in India is also animal-oriented and that needs to change too, she adds.
“When we talk of forests, we talk about the animals in them, never the plants. And when we do talk of plants, it’s only about agricultural crops or medicinal plants. We really need to increase awareness about the importance of wild plants.”
Prasanna et al 2020. Didymocarpus sinoindicus (Gesneriaceae), a new species from India and China. Rheedea 30(1): 78-85.
Prasanna and Gowda 2020. Rediscovery of four narrow endemic Didymocarpus species (Gesneriaceae) from Mizoram, India, with revised species descriptions and lectotypifications. Phytokeys 148: 1-19.
Cai et al 2016. Didymocarpus anningensis (Gesneriaceae), a new species from Yunnan, China. Phytotaxa 255 (3): 292-296.
Souvannakhoummane and Phonepaseuth 2020. Didymocarpus albiflorus (Gesneriaceae), a new species from Vientiane capital, Lao PDR. Taiwania 65 (2): 109-113.
Souvannakhoummane et al 2019. Flora of Nam Kading National Protected Area VI: Didymocarpus middletonii (Gesneriaceae), a new species from Limestone. Edinburgh Journal of Botany 76 (1): 45-54. doi:10.1017/S0960428618000264
Joe et al 2016. Didymocarpus moellerii (Gesneriaceae): a new species from northeastern India. Phytotaxa 266 (1): 057-060.
Lahiri et al 2020. Didymocarpus bhutanicus W.T. Wang (Gesneriaceae): a new addition to the herbs of India. Journal of Threatened Taxa 2 (4): 15514-15517.
Banner image: The Didymocarpus sinoindicus flower. Photo courtesy Preeti Saryan/ Rheedea.