This Geranium is in the database as G. versicolor lancastriense???

http://www.theplantlist.org/tp...
http://www.catalogueoflife.org...

You're correct. It should be listed as a synonym of G. sanguineum. I'll get it fixed. Thanks!

Thank you Kent.

I have a question. I'm just an amateur, but I have Geranium sanguineum

Something went wrong:

I have G. sanguineum , see http://seedsite.eu/images/Foto...

and I have G. sanguineum lancastriense (see picture)

The G. sanguineum is much higher and has a different color of pink than the G. sanguineum ' lancastriense'
How can gardeners know about which plant we are talking about if they have the same name, but a completely different appearance?

Nothing went wrong, G. lancastriense and G. sanguineum var. lancastriense are synonyms of G. sanguineum according to both of the sources you referenced in your original post. That's exactly how it is shown in the database.

Looks to be another one of those plants that have been lumped together. All are G. sanguineum, but have different bloom colors and petal styles.
http://en.wikipedia.org/wiki/G...

Yeah, wild species of plants tend to show quite a bit of variation among individuals. That's part of the joy of growing them.

I see why they sometimes give an added name for variations with the species. Just don't understand why they end up lumping them together.
Especially if each comes true to the parent plant from seed.

Because coming true from from seed isn't the standard for defining a species or even a variety. For example, Penstemon angustifolius plants normally produce blue flowers, but you can sometimes find white flowered individuals. In this species, white flowers are a recessive trait so if you grow white flowered plants in your garden and they are either self fertilized or fertilized by another white flowered individual, 100% of the seedlings will produce white flowers, i.e. they "come true" from seed. That doesn't make them a separate species or even variety. It's just part of the natural variation within the species.