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Why cannot most palm trunks grow thicker after they begin growing upward?

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Dense grove of acai palm trees (Euterpe oleracea) with slender trunks and abundant green fronds growing on Combu Island in Belem, Para, Brazil. — Palm Wild acai palms (*Euterpe oleracea*) growing on Combu Island in Belem, state of Para in Brazil.

Most palm trunks cannot grow thicker after they begin growing upward because they lack a cambium, or growing layer, which is responsible for secondary growth in woody broad-leaved plants.12

Unlike typical woody trees that increase in diameter through the production of new cells at a cambium layer, palms rely on a single growing point. Because they lack the mechanism to produce additional girth once they begin their vertical ascent, palms typically undergo an "establishment growth" phase, where the stem attains its maximum diameter below ground before it starts to grow upward.12

While some palms may exhibit localized swellings or "bellies," these are caused by an increase in the size or number of internal cells rather than the activity of a cambium layer. Consequently, the structural integrity of a palm is determined by its initial development rather than the continuous secondary thickening seen in other tree species.123