Two-thirds of this medicinal plant family has no indexed research, and most of its studied chemistry stops before human trials.
We tagged all 33,727 indexed studies of the Apocynaceae — the family of periwinkle, oleander and milkweed, and the source of the cancer drug vinblastine — across 50 dimensions. The research concentrates on the family's chemistry, does not reach two-thirds of its species, and covers the most threatened species least.
Every species in the family
We load every accepted Apocynaceae species from a taxonomic authority and link each to the indexed literature. A species with no linked papers is recorded as unstudied.
The Apocynaceae hold roughly 5,851 accepted species — climbing periwinkles, wax plants, oleanders, the milkweeds that monarch butterflies depend on. We link each to OpenAlex, tag every study with a panel of domain-expert models whose tags a second model checks, and place each study at its field site rather than its authors' address. The result is a map of what has and has not been studied in this family, species by species.
Mostly a search for chemistry
Two-thirds of Apocynaceae research is pharmacology and natural-products chemistry. Ecology, taxonomy and agriculture together account for a smaller share.
The family is a major source of monoterpene indole alkaloids — the class that includes vinblastine and vincristine — along with cardiac glycosides and flavonoids. Most studies use laboratory bioassays and spectroscopy; fieldwork is less common.
The gap between the lab and the clinic
Most of the evidence is early-stage. There are roughly a hundred times more lab studies than human trials.
30% of studies report a bioactivity — antimicrobial, antioxidant, anticancer, cardiovascular. Grouped by how far each study got toward proof in humans, the counts fall sharply at every stage. Each number counts distinct studies at that stage, so a single molecule may appear at more than one stage. 5,501 studies are at the cell- or enzyme-assay stage; 386 report human trials.
Two-thirds never studied
Behind the chemistry, 3,748 species — roughly two of every three — have no indexed research at all. Almost all the research goes to a handful of genera.
The family's largest genera are also its least studied. Hoya (the wax plants) has 533 species, 67% of them unstudied; Ceropegia (the lantern flowers), 432 species, 60% unstudied; Cynanchum, 75% unstudied; Matelea, 83%. In each of the largest genera, most species have no research.
Research runs opposite to extinction risk
Compare research with extinction risk and the pattern reverses: the more threatened a species, the more likely it has never been studied.
Among least-concern species, a third are unstudied. Among vulnerable species the share is three-quarters, and among data-deficient species 83%. Part of this may be structural: species are often listed as threatened because they are rare, narrowly ranged, or recently described — traits that also reduce how often they are studied — so the relationship is a correlation and may partly reflect those traits. Threats are addressed in 4% of studies.
Most of the family has no IUCN assessment: 4,976 accepted species have not been evaluated.
Where the research happens
Study sites cluster where the family is diverse and there is pharmacological interest — led by Brazil and India.
Brazil (761 sites) and India (689) lead — India through its long ethnopharmacological tradition, Brazil through the family's Neotropical diversity. Indonesia, China, and the United States follow, where the native milkweeds (Asclepias) carry a large literature of their own. Research concentrates where the family is richest and where there is a reason to look for drugs.
The unstudied species are elsewhere
Map instead where the never-studied species live, and the picture changes. India, second in research, ranks low for unstudied diversity; its research concentrates on a familiar, well-worked subset. The unstudied species cluster across tropical regions the literature has passed over: South Africa (259 unstudied species), Venezuela, Mexico, Colombia, Madagascar, Peru, and Papua New Guinea.
The two distributions differ. Research is concentrated in a few countries, while the unstudied species are concentrated in the Neotropics, southern Africa and Madagascar, and Melanesia.
Three imbalances in the record
Three imbalances in where research has and has not gone.
This atlas is one view of a complete, queryable corpus. A single genus's evidence profile, a country's Apocynaceae research, or a shortlist of unstudied threatened species to survey is each a query away, on the same reproducible foundation. A next step turns these gaps into a ranked survey list — scoring each unstudied species by the chemistry of its studied relatives, so a search can start where the chemistry is richest. The ranking orders where to look; laboratory work determines what each species holds.
Where to look next
The sections above measure what has and has not been studied. This section ranks the unstudied species by where the chemistry of their relatives is concentrated, to indicate where to look first.
Chemistry runs in families — closely related species tend to make the same kinds of compounds. So we score each unstudied species by how chemically productive its genus already is: the share of its studied relatives that have yielded a characterised bioactivity or compound. An unstudied species whose relatives are chemically productive ranks higher.
| # | Genus | Signature chemistry | Studied species that yielded chemistry | Unstudied left | Examples to start with |
|---|---|---|---|---|---|
| 1 | Strophanthus | Cardiac glycosides | 96% (24/25) | 14 | S. barteri, S. bequaertii, S. bullenianus |
| 2 | Kopsia | Monoterpene indole alkaloids | 94% (16/17) | 7 | K. angustipetala, K. harmandiana, K. rajangensis |
| 3 | Alstonia | Monoterpene indole alkaloids | 87% (33/38) | 6 | A. annamensis, A. curtisii, A. guanxiensis |
| 4 | Melodinus | Monoterpene indole alkaloids | 85% (11/13) | 10 | M. angustifolius, M. baccellianus, M. baueri |
| 5 | Tabernaemontana | Monoterpene indole alkaloids | 78% (63/81) | 43 | T. alfaroi, T. allenii, T. amplifolia |
| 6 | Aspidosperma | Monoterpene indole alkaloids | 74% (39/53) | 20 | A. castroanum, A. crypticum, A. darienense |
The top genus, Strophanthus, is the source of the cardiac glycoside ouabain, and has 14 unstudied species; Rauvolfia — the genus that gave medicine reserpine — sits just below this list, with 40 unstudied species. The ranking draws only on the chemistry recorded for each genus's studied relatives, and surfaces both from that alone.
A starter survey list
Unstudied species drawn from the top genera — a concrete place a screening lab or a taxonomist could begin. Grouped by genus.
Each name is a species with no indexed research, sitting in a genus whose studied relatives are chemically productive. Whether any of them holds a useful compound is determined by laboratory testing.