monoecious: having male and female flowers/flower parts on the same plant
This might be a good time to talk about flowers. Some flowers have both male (stamen) and female (pistil) parts in the same flower. These are considered “perfect” flowers. An “imperfect” flower is either only male (staminate) or only female (pistillate). A monoecious plant can have either perfect or imperfect flowers, but if they are imperfect both the staminate and pistillate flowers will be present.
The opposite of monoecious is dioecious, where the plant has either staminate or pistillate flowers, but not both. If you find yourself getting the two mixed up, it can be helpful to know that both terms are derived from the Greek “oikos” which means “house”; when combined with “mono” (one) or “di” (two), you get:
monoecious = one house
dioecious = two houses
In other words, in a monoecious plant the male and female flowers live together in one house (or plant) while in a dioecious plant you will only find one or the other.
The catkins in the photo are from an alder (my guess is Alnus tenuifolia) I saw on a hike. The male catkins are the pendulous ones while the female ones are more cone-like. Earlier in the spring they would have appeared fuzzy (the males) or small and green (the females), but as they pollinate/get pollinated they turn brown and harder.