Tatyana's Flowers are a special type of plant having red flowers and normally indistinguishable from a typical houseplant. Only the three potted plants in Constantine's bedroom (The Sword) can be confidently identified as Tatyana's flowers, due to their proximity to the Compendium of Natural Magic, on the table in the same room.
According to chapter 15 of the book, these flowers are native to the Esse Range; a frigid mountainous terrain. In order to survive, they have special properties that enable them to diffuse magic and to induce sleep (which explains why two plants are placed on either side of the bed). The nature of these abilities are unclear, but have been attributed to the "warming and swirling [of] the magical energy of the sentient plants and rocks". The name is derived from Tatyana Yokobik, an archemage who supposedly used these plants as a means of "temporary negation of magical spells and systems".