Hi Silversurfer,
It looks like they were both classified in the same genus at one time so it makes sense that the flowers look so similar. However, the flowers of Hippobroma longiflora are white and have much longer corolla tubes than Isotoma axillaris. The flowers in Floo's photo look pale blue or pale mauve and have the shorter corolla tubes that are consistent with Isotoma axillaris. Isotoma axillaris can be shades of blue, mauve-pink, or white. The foliage also has the daintier look of Isotoma.
Another observation is that this plant appears as if it is being cultivated in a public area. I would hope that most people would have better judgement than to plant the highly toxic Hippobroma in such an area, especially since a bit of sap in the eye can cause blindness. Of course, not everyone uses their better judgement.
Isotoma axillaris is also poisonous, but much less so according to what I've read.
