Spider Sundew Discovered in Madagascar

A discovery by Missouri Botanical Garden staff in Madagascar has resulted in the description of a new species of carnivorous plant. The spider sundew, Drosera arachnoides, gets its name from its habit of clinging to the side of cliffs, and the spider-like appearance of its hairy leaves. And it’s those very leaves that make this plant so deadly to its unsuspecting insect prey.

Missouri Botanical Garden staff discovered the spider sundew while doing field work in the Vohibe Forest of Madagascar, at a protected site managed by the Garden’s William L. Brown Center. During a visit to Tsitondroina waterfall in 2010, Brown Center ethnobotanist Nivo Rakotoarivelo noticed sundews growing near the top of the falls.

Tsitondroina waterfall in the Vohibe Forest of Madagascar. Photo by Research Specialist Nivo Rakotoarivelo.

Rakotoarivelo knew this plant was different than the other five species of sundew found in Madagascar. She tentatively identified it as a species affiliated with the more common Drosera indica, or simply Drosera sp. meaning species. L.R. Andriamiarisoa, who studies the mosses of the Vohibe Forest, helped with identification of the plants found nearby.

Dried plant specimens were collected and sent to Madagascar’s national herbarium, and the Missouri Botanical Garden Herbarium in St. Louis, where they were also digitized for the online database Tropicos®.

Nearly a decade later Andreas Fleischmann, a botanist with Botanische Staatssammlung München in Germany, studied those herbarium specimens and realized Rakotoarivelo and the rest of the Garden’s collection team had, in fact, found a new species. And it was endemic to Madagascar, meaning it is not known to occur anywhere else on Earth.

With work on a description of this new species underway, Rakotoarivelo along with Research Specialists Aina Razanatsima and Fortunat Rakotoarivony, went back to the waterfall to collect more information about the plant’s ecology and biology, along with new photos and additional herbarium vouchers.

Drosera arachnoides in flower. Photo by Research Specialist Aina Razanatsima.

Describing a New Species

The description of Drosera arachnoides as a new species was published in July 2020 in the journal Plant Ecology and Evolution. In addition to the collections made by Garden staff at Tsitondroina waterfall, Fleischmann uncovered another specimen collected almost 80 years earlier and nearly 200 miles away.

Using these specimens, the authors were able to show D. arachnoides occupied a different habitat than its close relative, D. humbertii, another Madagascar-endemic sundew. The spider sundew is a lowland species growing in tropical evergreen forests, while D. humbertii grows at higher elevations in the northern part of the country.

Fewer than 1,000 individuals of D. arachnoides have been found in the wild. And while the site at Tsitondroina waterfall is in a protected area, there is a risk human interference or natural events could quickly and dramatically reduce that population. The authors do point out the region is botanically under-explored, so it is likely more populations of Drosera arachnoides exist elsewhere in eastern Madagascar.

A digitized herbarium voucher of Drosera arachnoides from the Missouri Botanical Garden Herbarium. Via Tropicos®.

The Vohibe Forest

The Vohibe Forest is 12 square miles of low- to mid-elevation rainforest located on the eastern slope of Madagascar. The area is home to 11 species of lemur, including the critically endangered Indri indri, a large lemur known for its “singing” behavior.

Vohibe Forest also contains nearly 900 known plant species, almost 80% of which are endemic to Madagascar. This high level of endemism and biodiversity makes the Vohibe forest a priority for conservation.

The Garden’s William L. Brown Center has managed an ethnobotany program in the Ambalabe community within the Vohibe Forest for more than a decade. The program works to train Malagasy graduate students in ethnobotanical study, and works with the local community on sustainable use of natural resources and conservation of the environment.

Rakotoarivelo says, “The success of our work at Vohibe forest is due to the close collaboration and the involvement of the local community. Community members are involved in conservation activities such as forest restoration and environmental education. Their help during our field trips is also valuable by serving as guides in the forest. We could not do our botanical work without their participation.”

The Vohibe Forest is one of a wide network of sites in Madagascar the Missouri Botanical Garden works to conserve. The program has more than 150 staff, of whom almost all are Malagasy. Since being permanently established in the 1980s, the program has collected and recorded nearly 900 new species for the Garden’s herbarium.

See also — Spotlight on Science: Armand Randrianasolo

Ambalabe village in Madagascar. Photo by Rainer Bussmann.

What is a Sundew?

Sundews are carnivorous plants, in the same botanical family as the Venus fly trap. About 250 species of Drosera can be found across the globe, on every continent except Antarctica. With the discovery of the spider sundew, there are now six known species of Drosera found in Madagascar, two of which are endemic.

These plants trap insects with glue-like hairs on their leaves, dissolving their prey and absorbing its nutrients. The carnivorous diet of these plants is considered an adaptation to the nutrient-poor soils in which many of these species grow. The sticky droplets resemble morning dew, a trait reflected in both the plant’s botanical and common names.

Their carnivorous nature and glistening droplets make sundews popular in cultivation, however they can be difficult to grow because of environmental requirements. The Missouri Botanical Garden cultivates about a dozen species in its living collection, many of which are on display in the Schoenberg Temperate House.

Cassidy Moody
Senior Digital Media Specialist

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