I was given the pictured plant as a cutting from a colleague who also received it as a gift, but without a name. It is a spectacular specimen about a foot and a half high with a long woody stem (pictured). From the moment it started flowering a couple of years ago, it has not stopped--winter or summer (also pictured).
It thrives in a sun-bathed, south-facing window and enjoys twice-weekly waterings.
Your identification is convincing, vngarden. Common names include Crown of Thorns, Christ Plant and Christ Thorn.
After searching further, I remain unsure whether it is Euphorbia milii var. splendens or var. imperatae. It is not clear to me if the leaf shape is variable or the slightly inset tip on my plant is indicative of one variety or another. More photos of var. imperatae show a similar leaf, but occasionally some images come up under the (possibly) more common var. spendens.
I will mark this as solved, but if anyone can distinguish the variety, the refinement would be appreciated.
I have this plant within my grandmother's garden. It is very old, approximately 40 years. It flowers a vibrant color of red, and I do not recall ever seeing new blooms in a lighter shade or varying color, as within your photo. It stands approximately 3 to 3.5 feet tall, and it spreads above ground in a peculiar fashion (perhaps due to being in a white marble rock garden). It is not currently in bloom, but I expect it to be soon. I have one or two photos of it in bloom and will post them for comparison, once I can locate them (I am a photographer, so it will be like finding a needle in a haystack...I took it long ago).
Edit: I just walked out there and noticed blooms, but I do think it was dormant for a while, due to the irrigation system being in need of repair and our prolonged drought. It has an extremely heated southern exposure for approximately half the day, and usually receives watering every day with our typical afternoon showers, simply not this past year.
Cheerful, these may not help you much. They were taken with a beach trashed Xsi, and I was attempting to focus upon the flowers themselves. I will take some better ones for you this week, ensuring I detail the leaves and entire plant, posting them later in the week. I am curious as to their difference.