De castanea

Castanea, ut dicit Ysidorus, arbor est, cuius fructus gemini in modum testiculorum infra folliculum reconditi iacent. Qui cum eiciuntur quasi castrantur, et inde nomen accepit castanea. Hec arbor simul ut excisa fuerit, tanquam silva simul expullulare consuevit.

The chestnut tree, as Isidore said, is a tree, of which the twin fruits hang in the manner of testicles hidden below in the scrotum. When such are cast down, it is as though they are castrated, and from there it received the name chestnut. As soon as this tree will fall, a forest will grow from its seeds.

castanea, castaneae f. n. a chestnut (tree)
castrō, castrāre, castrāvī, castrātum v. to prune; amputate; punish; purge; castrate
cōnsuēscō, cōnsuēscere, cōnsuēvī, cōnsuētum v. to accustom, tend to, habituate; to have sex with
ēiciō, eīcere, ēiēcī, ēiectum v. to thrust, cast, drive out; expel, reject; to exit; to run (a ship) aground
excīsus, excīsa, excīsum part. collapsed; escaped; destroyed; disappeared
expullulo, expullulare, (???), (???) v. to grow lots of offspring
folliculus, folliculī m. n. (Late Latin) sac; urinary bladder; scrotum
geminus, gemina, geminum adj. twinborn, twin; doubled, pair, both; resembling, similar, like
infra adv. below
reconditus, recondita, reconditum (comp. reconditior) v. concealed; hidden
tanquam adv. (just) as; as it were, so to speak; as much as; such as; for instance
testiculus, testiculī m. n. (anatomy) a testicle; (figuratively) manliness

Ysidorus: Isidore of Seville was an archbishop and scholar from Roman-occupied Spain who studied and wrote about theology, among other topics. His Etymologiae acts as a sort of early encyclopedia; being such it covers a wide array of topics, including the logistics of linguistics, society, natural and applied sciences, and art.

cuius . . . iacent.: Isidore describes the chestnut as resembling a set of testicles. A chestnut burr may contain up to seven nuts, held in a similar manner to the two (or one, or three?) testicles in the scrotum.

Hec: In Late Latin, ae is commonly shortened to e.

simul ut . . . simul: Here, this is best translated as “as soon as.”