Carnivory in plants did not evolve once but at least eleven times, in separate families with no close relationship to one another. This guide draws a sharp line within that history: it includes only the ten genera whose trap catches prey, digests it itself, and is visible above ground and above water. Everything outside that line gets its due here once — not as full species pages, but as an account of where the boundary lies and why.

Utricularia — bladderworts

With around 250 species, the bladderworts form the largest genus of all carnivorous plants, comfortably outnumbering Drosera and Nepenthes combined. Species grow worldwide, from free-floating aquatics to epiphytes in humid rainforest and tiny terrestrial forms in waterlogged soil. The trap is a hollow bladder sealed by a trapdoor and held under negative pressure; when a small prey animal brushes the trigger hairs at the opening, the door springs open in a fraction of a millisecond and sucks the animal inside — one of the fastest movements known in the plant kingdom. This guide still leaves the genus off its species list: the bladders sit underwater or underground, and so are not the visible trap the other ten genera show. This guide's trap-mechanism list already reserves a code for it (BLAAS), so the genus could be added without rebuilding the site should that boundary ever move.

Underground and underwater: Genlisea, Philcoxia and Aldrovanda

Three further genera fall outside the guide for the same reason as the bladderworts. Genlisea (around 30 species, tropical Africa and South America) has underground, spiral-shaped leaves forming a lobster-pot trap: tiny soil organisms can enter but cannot find their way back out. Philcoxia (7 species, the Brazilian cerrado) traps in a similar way with sticky leaves hidden just beneath the sand. Aldrovanda, the waterwheel plant, is the only aquatic snap-trap plant — a close relative of Dionaea with an almost identical, lightning-fast action, but floating just below the surface of nutrient-poor pools. All three meet the same limit as the bladderworts: the trap exists and works convincingly, but is not visible above water or above ground.

Catching without digesting: Roridula and Triphyophyllum

Roridula (2 species, South African fynbos) has sticky, resin-covered leaves that trap insects just as effectively as Drosera does — but the plant produces no digestive enzymes and does not absorb the nutrients directly. Instead, a specialised assassin bug, Pameridea, immune to the glue, lives on the plant and drains the trapped prey; the plant in turn absorbs nitrogen from the bug's droppings. It is the textbook borderline case: a trap that works flawlessly, paired with an animal that takes over digestion. Triphyophyllum peltatum (1 species, West African rainforest) is carnivorous for only one phase of its life: as a young plant it grows sticky trapping leaves, before switching to the non-carnivorous, climbing leaf form with which it grows as a liana high into the forest canopy. Neither species meets this guide's double requirement — catching prey and digesting it, for the whole of its life — so neither gets a page of its own.

Protocarnivorous plants: Stylidium, Brocchinia, Catopsis, Passiflora and Saxifraga

Further still from the core lie the so-called protocarnivorous plants: plants that trap or kill insects, but for which digestion, absorption, or even the benefit to the plant remains unproven or disputed. Stylidium (trigger plants, over 300 species, mostly Australian) has glandular hairs that hold insects fast and may secrete digestive enzymes, alongside its better-known trigger-style column that flicks pollinators. Brocchinia and Catopsis, two bromeliad genera from South and Central America, form a water-holding tank with their leaf rosette in which insects drown; some species have a smooth, waxy inner wall that improves the trap, and there is evidence of bacterial breakdown from which the plant may benefit. In a small number of Passiflora species (passionflowers), sticky bracts below the flower trap insects, likely mainly in defence against flower predators rather than as a feeding strategy. A few Saxifraga species have sticky, insect-trapping leaf hairs for the same disputed reason. None of these genera meets the requirement that the plant itself both catches and digests its prey; that is why none gets species pages here, even though each belongs to the fuller story of how often, and how differently, catching animals has been tried across the plant kingdom.