Drosera arachnoides is a Malagasy sundew whose long, hairy leaves and position against steep wet surfaces inspired the name spider sundew. Its story combines modern fieldwork with a much older herbarium collection, showing how a plant can remain unrecognised even after specimens have entered scientific collections.
Discovery and recognition
Kew accepts Drosera arachnoides Rakotoar. & A.Fleischm., published in 2020, and records its native range as Madagascar. It is an endemic species: that term concerns its natural geographical range, not how many plants might eventually be propagated elsewhere. Kew taxonomic account.
The Missouri Botanical Garden's account explains that Nivo Rakotoarivelo noticed the unusual sundew during fieldwork in Vohibe Forest in 2010. Subsequent work connected those plants with an older specimen collected in 1941 at another Malagasy locality. Field observations, photographs and preserved material together supported recognition of the species. Missouri Botanical Garden discovery account.
The later name does not mean the plant began to exist in 2020, nor that every earlier identification was based on a careless observation. Taxonomic recognition often depends on bringing scattered evidence together and comparing it with the appropriate relatives.
Distinguishing features
The original description identifies a perennial with a short, condensed stem, numerous narrow leaves and persistent older foliage. Typical leaves measure 22–40 mm long. The upper petiole surface carries conspicuous pale, non-glandular hairs. Relative to D. humbertii, the authors emphasise more active leaves, denser petiole hair and a different arrangement of old leaves. Its spider-like appearance is descriptive; it is not evidence that the plant shares the annual lifestyle of Arachnopus sundews. Original botanical description.
For identification, separate the sticky tentacles of the trapping blade from ordinary hairs on the leaf stalk. A photograph that makes every hair look like a carnivorous gland loses an important distinction. Whole-plant photographs should also show how the older leaves remain around the stem.
Forest wetlands rather than a generic mountain climate
The paper records plants on wet rock and soil near waterfalls, in both dappled light and more exposed positions. Known records extend from lower and middle elevations to an older mountain collection. The authors contrast that ecology with the higher mountain habitats of D. humbertii. They record flowering and fruiting specimens in September and October, during the local cooler season.
This matters when interpreting the broad “seasonally dry tropical” biome label on a database page. Regional seasonality and moisture immediately around a waterfall are different scales of description. A seasonal climate label alone cannot justify drying a cultivated plant's roots.
Conservation evidence
In their 2020 paper, the authors assessed the species as Vulnerable under IUCN criteria. That is a dated assessment within the description, not a claim that this draft has established a new current population count.
The Botanical Garden explained that fewer than 1,000 individuals were known at the time of publication. It also noted that the region was incompletely explored and additional populations could exist. A small known population and incomplete survey coverage can both be true. Neither uncertainty cancels the value of protecting the documented habitat. Botanical Garden conservation context.
What can be said about cultivation
The material reviewed for this account supports natural history and identification much more strongly than a detailed cultivation recipe. Warm conditions and a dependable supply of moisture are reasonable ecological starting points, but exact temperatures, soil ratios, dormancy treatments and cutting success remain unverified here.
For propagated material, retain the source's successful growing history and distinguish observations from assumptions. Record new-leaf development, root disturbance, flowering and any attempted propagation. Do not replace missing species evidence with a pygmy-sundew or petiolaris-complex routine merely because the plant is hairy.
The value of this species account lies in keeping its distinctive identity, forest-waterfall ecology and conservation history together. Future documented cultivation results can expand that picture without rewriting uncertain guesses as established facts.
Nano Nursery Drosera Encyclopedia — species profile. Related core chapters: 5, 14 and 29. Reviewed 23 September 2026. Cultivation guidance concerns established plants; recently deflasked plants need separate acclimatisation.
