noun, plural prothallia [proh-thal-ee-uh] .
Botany. the gametophyte of ferns and related plants.
the analogous rudimentary gametophyte of seed-bearing plants.

1855–60; < Neo-Latin < Greek pro- pro-2 + thallíon, diminutive of thallós young shoot; see -ium

prothallial, prothallic, prothalline [proh-thal-een, -ahyn] , adjective
prothalloid, adjective Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
prothallus or prothallium (prəʊˈθæləs, prəʊˈθælɪəm)
n , pl -li, -lia
botany the small flat free-living gametophyte that bears the reproductive organs of ferns, horsetails, and club mosses. It is either a green disc on the soil surface or it is colourless and subterranean
[C19: from New Latin, from pro- before + Greek thallus a young shoot]
prothallium or prothallium (prəʊˈθæləs, prəʊˈθælɪəm, -laɪ, -lɪə)
[C19: from New Latin, from pro- before + Greek thallus a young shoot]
pro'thallic or prothallium
pro'thallial or prothallium

Collins English Dictionary - Complete & Unabridged 10th Edition
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Encyclopedia Britannica


the small, green, heart-shaped structure (gametophyte) of a fern that produces both male and female sex cells (gametes). The prothallium forms from a spore. After fertilization, a young sporophyte plant develops; it consists of a primary root, primary leaf, the rudiment of a new stem, and an organ, called a foot, that absorbs food from the gametophyte.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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