Seeds & Dispersal — Travel Without Moving
How plants engineer flight, explosions, ocean voyages, and animal taxis to colonise the world
1 The Biological Imperative: Why Disperse?
Plants are sessile organisms — they are rooted in one place — yet their long-term survival depends on whether they can send offspring to new locations. Seed dispersal solves three critical problems:
- Competition avoidance — Seedlings growing directly beneath the parent plant must compete for light, water, and soil nutrients.
- Pathogen escape — Herbivores and pathogens concentrate near adult plants (the Janzen–Connell hypothesis).
- Habitat colonisation — Reaching new, unoccupied sites increases the species' geographic range and genetic diversity.
Key insight: Because plants cannot walk, they have evolved an extraordinary toolkit of anatomical and morphological adaptations that exploit physical forces (wind, water, gravity) and biological vectors (animals) to move their seeds — sometimes thousands of kilometres.
2 The Five Canonical Dispersal Modes
| Mode | Scientific Term | Vector | Key Adaptations | Classic Example |
|---|---|---|---|---|
| 🌬️ Wind | Anemochory | Air currents | Wings (samaras), plumes (pappus), dust-like seeds | Maple, dandelion, orchid |
| 🌊 Water | Hydrochory | Rivers, ocean currents | Buoyant husks, waterproof coats, air-trapping fibres | Coconut, mangrove |
| 🐾 Animals (external) | Epizoochory | Fur, feathers, clothing | Hooks, barbs, sticky mucilage | Burdock burr |
| 🍒 Animals (internal) | Endozoochory | Gut passage | Fleshy, nutritious fruit; hard seed coat resists digestion | Cherry, fig, mistletoe |
| 💥 Explosive | Ballochory | Self-generated force | Turgor pressure, hygroscopic tension, elastic tissue | Squirting cucumber, Cardamine |
A sixth mode, barochory (gravity), is sometimes listed separately — heavy fruits simply fall and roll downhill.