What this all means exactly, that’s the point, so I’ll make a point of defining any unfamiliar terms listed here.
Spike = An unbranched, elongated inflorescence with sessile or subsessile flowers or spikelets maturing from the bottom upwards.
Raceme = An unbranched, elongated inflorescence with pedicellate flowers maturing from the bottom upwards.
The following native genera/species have catkins:
Alnus spp., Betula spp., Corylus cornuta (Betulaceae)
Salix ssp., Populus spp. (Salicaceae)
Quercus alba (Fagaceae)
Herbaceous species can also display catkins – stinging nettle (Utrica dioica) is one example.
Catkins are, by definition, imperfect then. Either staminate (male) or carpellate/pistillate (female). The majority of those listed above only display catkins for the flowers of one sex – male, with the female flowers of another form.
A photograph of the female inflorescence (strobile) above and the male catkin below of red alder (Alnus rubra). Strobile = an inflorescence resembling a cone.
The willow family is an exception possessing both male and female catkins.
Here is an example of a carpellate Pacific willow (Salix lucida) catkin:
The willow family is also the only dioecious family listed above, with male and female inflorescences occurring on separate plants.
