PYXIDIUM
pyxidium, pyxis
(noun) fruit of such plants as the plantain; a capsule whose upper part falls off when the seeds are released
Source: WordNet® 3.1
Etymology
Noun
pyxidium (plural pyxidia)
(botany) A seed capsule in the form of a box, the seeds being released when the top splits off.
Source: Wiktionary
Pyx*id"i*um, n.; pl. Pyxidia. Etym: [NL., fr. Gr. Pyx.] (Bot.)
(a) A pod which divides circularly into an upper and lower half, of
which the former acts as a kind of lid, as in the pimpernel and
purslane.
(b) The theca of mosses.
Source: Webster’s Unabridged Dictionary 1913 Edition