I went down a bit of a rabbit hole recently.
A friend who knows far more about butterflies than I do commented that seeing lots of Red Admirals usually means there are nettles nearby. That didn't make sense at first. We don't have ongaonga on site and I hadn't noticed any common nettles either.
The breakthrough came when I realised a plant I'd initially thought was galinsoga was actually Asthma Weed (Parietaria judaica).
Asthma Weed belongs to the nettle family (Urticaceae), though not a true stinging nettle. Once I worked that out, the butterfly comment made a lot more sense. Surveys of butterfly host plants in New Zealand include both Urtica nettles and Parietaria species. [catalogue....ta.govt.nz], [nzbutterflies.org.nz]
kahukura Red admiral butterfly Vanessa gonerilla
Spotting the difference
The confusion wasn't helped by the fact that Asthma Weed and Galinsoga can look surprisingly similar at a quick glance. The easiest way to tell them apart is:
Asthma weed (Parietaria judaica)
Leaves alternate up the stem.
Tiny greenish flower clusters.
No obvious white petals.
Member of the nettle family. [plantref.org]
Galinsoga (Galinsoga parviflora)
Leaves occur in opposite pairs.
Tiny daisy-like flowers.
Yellow centre with usually five white ray florets.
Member of the daisy family. [massey.ac.nz]
Why the butterflies mattered
The lesson for me was that sometimes a field observation points you in the right direction, but not how I expected. I was looking for "nettles" and mentally picturing ongaonga. What I actually had was another nettle cousin hiding in plain sight.
A useful reminder that plant identification often starts with asking why something in the ecosystem is there. In this case, the butterflies were the clue