Most orchids have leaves at some point in their life cycle, so it is not a reliable characteristic unfortunately. Orchids will always have floral part in multiple of 3, 3 sepals + 3 petals, whereas most other flowering plants occur in multiples of 4 or 5. This can be a bit hard to see sometimes as orchids often have fused petals/sepals (as in greenhoods). Typically one of the petals is highly modified (the labellum) and looks unlike the other flower parts.
As for suggesting taxa, go for it. If you are wrong you might get an opportunity to learn some more about it. It also allows moderators to make other suggestions which in turn alerts the moderators of the relevant categories.
There are at least three tall (as opposed to prostrate) species of Lobelia in the ACT. Unfortunately the flowers of all are very similar. In a good season, you can tell the two more common species apart by the leaves. One (dentata) has toothed (dentate) leaves. The other (gibbosa) has smooth edged leaves. However, the bigger leaves in most seasons are gone by the time the flowers come.