Perennials 18—60 cm tall. Tap roots elongated, not thickened, up to 1 cm thick, lateral roots always tuberous, with tubers fusiform, oblong or even spherical. Caudex branched, 2-6 cm long; stems glabrous. Lower leaves triternate, leaﬂets segmented several times; segments 134-340 in number, linear or ﬁliform, ﬁnal segments 0.5-3.8 cm long, 0.5—8 mm wide, glabrous on both sides, but sometimes covered with bristles along veins above. Flowers solitary and terminal; involucrate bracts 1—3 in number, leaf—like; sepals 4 or 5, rarely 3 in number, all rounded or one, or occasionally two of them, caudate at the apex, 1-1.5 cm long, 0.7—1 cm wide, green but purple—red at the periphery or entirely purple-red, densely hispidulous, rarely glabrous on the abaxial side; petals 6-8 in number, consistently red, obovate, 2—4 cm long, 1.5—2 cm wide, rounded, 2—l0bed or incised at the apex; ﬁlaments entirely yellowish white, pink below but yellowish white above to entirely purple-red; anthers yellow; disk fleshy, waved, 1 mm high, yellow; carpels 1—3, but more frequently 2 in number, ovoid, always tomentose, hairs green, yellow to totally purple—red, c. 1 mm long; stigmas sessile, red, 1—1.5 mm wide. Follicles ovoid.
Chromosome number: 2n=10 (diploid)
Usually growing in steppes, meadows, open sandy dunes, shrubs, or at the edges of forests. Paeonia tenuifolia seems to prefer dry habitats, and was found growing at lowlands below an altitude of 900 m. Armenia, Azerbaijan, Bulgaria, Georgia, Romania, Russia (the Caucasus), Serbia, Turkey (European part) and Ukraine.
Paeonia tenuifolia as circumscripted here is a very distinct species. It has the ﬁnest leaflets/leaf segments and the greatest number of leaflets/leaf segments of any peony species. There is no intergradation with any other species. In Kartli, Georgia, it grows together with P. daurica. According to preliminary results from our DNA sequencing, P. majko Ketsk. is a hybrid between these two species.
Paeonia biebersteiniana was recognised as an independent species because it was described (e.g., by Schipczinsky (1937)) as having leaf segments that are wider than those of its close relatives. Paeonia carthalinica was distinguished from P. tenuifolia by its wider leaf segments and greyish pubescence on carpels. Hong and Zhou (2003) critically observed the variation of P. tenuifolia in three natural populations in the Caucasus. Leaf segments were found to vary continuously from 0.5 to 6.0 mm in width; even within an individual, three shoots had leaf segments of differing widths (1.5, 3.5 and 5.5 mm). The colour of hairs on the carpels was also very variable, from yellowish green to pink, red and purple red. Apparently, both P. biebersteiniana and P. carthalinica are within the variation range of P. tenuifolia (Hong & Zhou, 2003).
Even Anderson (1818) discovered variation in the width of leaf segments. He stated, “The sterile or rather the radical leaves in rich ground almost constantly assume a linear-lanceolate form; indeed both descriptions of leaves (linear or linear-lanceolate) are frequently produced on the same root”, and thus, “P. hybrida of Pallas is not even a permanent variety”. Unfortunately, many later authors (Ruprecht, 1869; Lipsky, 1899; Busch, 1901; Schipczinsky, 1937; Kemularia- Nathadze, 1961; Halda, 1997, 2004) paid no attention to Anderson’s words, and still recognised P. hybrida and P. biebersteiniana.
When Kotov (1956) described Paeonia lithophila as new, he stated that the new species differed from P. tenuifolia in having shorter stems (10-20 cm), shorter leaf segments (1-8 mm long) and smaller carpels (ca. 1 cm long, 1-1.5 cm wide). We examined a topotype, Kotov & Karnauch 19 May 1948 (PE), which is 22 cm tall, with the longest ﬁnal leaf segments reaching 12 mm. In addition, our collection D. Y. Hong & S. L. Zhou H99028 (from Kartli, Georgia) is 30-45 cm tall, with the longest ﬁnal leaf segments reaching 23—30 mm; H99043 (Kartli, Georgia) is 40—56 cm tall, with the longest ﬁnal leaf segments reaching 25-38 mm; but H99052/53 (Stavropol, Russia) is 19-29 cm tall, with the longest leaf segments reaching 18—25 mm. It is clear that P. tenuifolia also varies both in height of stems and length of leaf segments, with H99043 at one extreme, the holotype of P. lithophila at the other extreme, and the topotype and H99052/53 in the middle, linking the two extremes.
- Hong, De-Yuan. “Peonies of the World. Taxonomy and phytogeography.” Kew: Royal Botanic Gardens, 2010, p. 210-212.