Oxalis alpina (alpine woodsorrel) is monoecious: male and female parts occur on the same flower.

To prevent self-fertilization, this plant has thrum (stamens above styles) and pin (styles above stamens) arrangements of the floral parts.

An insect foraging for nectar would collect pollen on different parts of its body; pin pollen would be deposited on thrum stigmas, and vice versa.