prothallus

pro·thal·lus  (pr-thls) or pro·thal·li·um (-thl-m)

n. pl. pro·thal·li (-thl) or pro·thal·li·a (-thl-)

A small, flat, delicate structure produced by a germinating spore and bearing sex organs. It is the gametophyte of ferns and some other plants.

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[New Latin : pro-² + Greek thallos, shoot (from thallein, to sprout).]

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pro·thalli·al (-l-l) adj.

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prothallus  (pr-thls)

Plural prothalli (pr-thl)

The gametophyte of homosporous ferns and some other plants. Prothalli have chlorophyll for photosynthesis, but they are not differentiated into roots, stems, or leaves. They are usually small, flat, and delicate. Prothalli develop from germinated spores, and they bear both archegonia for producing eggs and antheridia for producing sperm. See more at alternation of generations.