Word of the Week: Strobilus

strobilus [ stroh-bahy-luhs ] noun, plural strobili: cone-shaped mass of ovule- or spore-bearing scales or bracts; reproductive structure of conifers

 

Tsuga canadensis (eastern hemlock) strobili: yellow male strobili along leaf axils (left); green female strobilus at branch terminal (bottom right); and ripening brown seed cone (center). Photo © Elaine Mills

Some seed-producing plants, like conifers, cycads and gingkos, do not have flowers and fruit. Instead their reproductive structures are strobili: microstrobilus (in place of male flowers) and megastrobilus (in place of female flowers and fruit).  

The male strobilus (commonly called a pollen cone) produces pollen grains, which are dispersed by the wind so that they can reach female strobili on other trees of the same species. After it releases its pollen, the microstrobilus dies away. Although male strobili look similar in structure from conifer to conifer, female cones are larger and distinctive among the species.

The female strobilus (also known as an ovulate cone or seed cone) contains ovules, which in the Pinaceae (pine family) are located in pairs side-by-side on the surface of each scale. After fertilization, each ovule develops into one seed. A pine seed cone may take two to three years to mature and may remain on the tree of some species for more than ten years before it drops to the ground. To keep its seeds viable during this time or even after it falls to the ground, it can close its scales in cold, windy, or wet weather–submerged in water this takes less than 30 minutes. Scales open when the weather is warm and dry enough for seed dispersal by wind or animals or for germination. We may easily recognize the female strobili of pine, but people often mistake the seed cones of some species like juniper and yew for berries. The fleshy seed cone of cypresses (and sometimes junipers) is also called a galbulus.

Strobili of Various Conifers

Other Strobili

Hops, used in beverages like beer, are the flowers of the climbing, herbaceous perennial Humulus lupulus and are called strobili.
Photo © Elaine Mills

The spore-producing structures of Equisetum hyemale (horsetail), a non-flowering evergreen perennial, are called strobili.
Photo © Elaine Mills

Reference

Arnett M. 2016. Unlocking the Secrets of the Pinecone. Scientific American. [accessed 2021 Jan 16].

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