The Sessile Wager

The sessile wager is a phrase coined by Botany for the Curious. It is a metaphor, not a theory: think of a rooted plant as having placed a bet when it germinated. From then on it mostly stays where it is, so pollination, dispersal and defence, problems that animals handle by moving, have to be solved some other way.

Why "sessile"

In plant description, sessile means sitting close, without a stalk; the word comes from the Latin for sitting. The phrase borrows that root sense: a rooted plant sits where it germinated.

Where it applies

The wager frames questions about rooted plants: how pollen gets from one flower to another when neither flower can travel, how a seed gets away from its parent, how a plant that cannot run resists being eaten. It frames the question, and research has to answer it. A trait is described as a solution only when evolutionary or functional research supports that reading, and the page leaves room for other explanations: developmental constraint, historical accident and artificial selection.

Where it does not apply

The wager is not used for floating plants, which do not fit the picture of a plant held in one place. It is not used for what people do to plants either. Pruning a garden and processing tea leaves act on a single plant or a picked leaf, and breeding a cultivar is selection by people; none of them is a solution found by the plant.

It is not stretched to every trait of a rooted plant. It covers pollination, dispersal and defence, so the angle between one leaf and the next on a stem, for example, is not framed as a wager.

How Botany for the Curious uses it

Botany for the Curious uses the phrase to ask how a rooted plant handles one of those three problems, and the wording marks it as a metaphor each time, as in "think of it as a wager". Each use is paired with research on the trait in question, and the research decides the answer.

The first use, on a page about sunflower heads, asks whether the sterile ray florets around the rim of the head help with pollination. A 2019 study of Anacyclus, another genus in the daisy family, by Cerca and colleagues found that heads with rays drew significantly more visitors. Those heads did not set more seed than heads without rays, which made up the difference with more florets, so the support is partial, and the page says so.

The guide's other coined phrase with a page of its own is leaf grammar.

Source

The definition of sessile follows B. D. Jackson, A Glossary of Botanic Terms, 4th edition, revised and enlarged (London: Gerald Duckworth; New York: Hafner Publishing, 1928; reprinted January 1953), entry "sessile".