I was just wondering, the english singular-plural things, are they derived from Latin? As in alga-algae, which fits into Latin, female nominative (femina-feminae), but I've also heard people say cactae as the plural of cactus (among other things), which doesn't fit into Latin (because -us is male nominative singular and -ae is female nominative plural).
The plural form of "cactus" is "cacti", although "cactuses" is also accepted. I've never heard the plural form you have mentioned.
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I've actually heard people say that. Cacti works with Latin though.

credo in Unum factorem coeli et terra