secondly

adverb

after the first

Wiktionary

Pronunciation: /ˈsɛk.(ə)ndli/ / /ˈsɛk.(ə)ntli/ / /ˈsɛkəndli/

adv

Etymology: Etymology tree English second Proto-Indo-European *leyg-der. Proto-Germanic *līkąder. Proto-Germanic *-līkaz Proto-Germanic *-ê Proto-Germanic *-līkê Proto-West Germanic *-līkē Old English -līċe Middle English -ly English -ly English secondly From second + -ly.

In the second place.
“Firstly, I continue to base most species treatments on personally collected material, rather than on herbarium plants. […] Secondly, I continue to base my concepts on intensive study of a limited suite of collections, rather than superficial study of every packet that comes to hand.”