Coniferous is to Conifer
Deciduous is to ?
Assuming just tree species here, since that seems to be the intent.
It doesn't parse exactly. Coniferous means cone-bearing, as does conifer.
But. Deciduous means 'dropping leaves', like an oak tree. Except that there are species of trees that are "cousins", i.e., in the same genus, where some species are deciduous, some are not. Plus there are conifers, American Larch as an example, that are deciduous.
So, there is no 'deciduous' group which is completely distinct from conifer.
What are you driving at?
Coniferous is to Conifer as Deciduous is to The Decider! (Jon Stewart fans rejoice)
I'm simply asking what the noun root of the adjective deciduous is.
A conifer is so because it is coniferous.
A ? is so because it is deciduous.
There's a Latin verb "decidre", which means "to fall off". There's no English form of the word. While "conifer" has Latin roots, ("coniferae" is the family name), the origins are in the Greek Konos.
When you're asking in the Bio section, adding the one word "noun" would have made it clear. sorry.
Ah - conifers are a family.
So, I can't meaningfully say "the conifers are a more primitive plant form than the decidres".
Separate names with a comma.