The Green Thumb’s Glossary: From Y-Z

For invasive species, yield is particularly important because their high growth rates and prolific reproductive yields enable them to dominate resource use, spread rapidly, and displace native vegetation.

For example, great mullein (Verbascum thapsus) can produce up to 240,000 seeds per plant, which remain viable in the soil for very, very long periods (seeds dating back to 1300 A.D have been successfully germinated). The long-lived seed bank and high reproductive capacity of this species makes it very difficult to eradicate.

Similarly, purple loosestrife (Lythrum salicaria) produces around 2.5 million seeds per plant in one season! The seeds have a very high germination rate that remain viable in the soil and underwater for many years. This high yield of seeds allows the species to outcompete native species and form dense stands.

Zygomorphic floral structure, when compatible with local generalist pollinators, can make invasive species highly successful — because they still reproduce effectively while potentially reducing pollination for native plants.

For example, scotch broom (Cytisus scoparius) has zygomorphic pea-like flowers. Bumblebees and honeybees can trigger their “spring-loaded” flowers, increasing their chance of pollination. This allows it to produce abundant seeds, forming dense stands that outcompete native vegetation.