USDA Z5, Lamoine, ME
someone else has suggested that it is Trillium chloropetalum rather than T. sessile.
I'm just glad to finally see it in flower!
Fermi de Sousa,
Central Victoria, Australia
Min: -7C, Max: +40C
From my admittedly limited experience with trilliums, I thought that the leaves on the chloropetalum were more up-turned and the edges potentially more wavy than those of the sessile species.
Based solely on the photos, I would have made the ID as T. sessile.
Certainly there are folks that have a great deal more experience with Trilliums than I, so hopefully they can provide you with a more concrete identification.
I don't have an opinion for you, Fermi, and I am still unsure of what my "T. sessile" really is. I bought it as T. sessile, and never gave it a second thought until I dug it up to divide it, and discovered the rhizome was not horizontal as it is supposed to be. My plant had several offsets, tightly held against the mother "bulb".
A friend sent me some plants of wild T. sessile and T. cuneatum from Illinois, which also has horizontal rhizomes.
Cuneatum had what I envisioned would be the typical horizontal growth:
But then I saw what he sent me as T. sessile:
They certainly looked vertical to me, but upon closer inspection I saw the horizontal rhizome:
It seems one of the better ways to distinguish species is with stamen and ovary characteristics, but the root configuration will certainly help. Not that you should dig yours up, but if you remember what it was like when you planted it, or for future reference.
Rick Rodich zone 4a. Annual precipitation ~24 inches
near Minneapolis, Minnesota, USA
The "themids" are in flower in our Southern Hemisphere garden.
I found a packet of corms of Triteleia (?laxa) 'Allure' which had been missed when planting out bulbs last fall
So they were planted in October when others of their clan were already in flower. Surprisingly not only did they grow but they have now come into flower