The taxonomic identity of the 30,000-y-old plant regenerated from fruit tissue buried in Siberian permafrost

Yashina et al. (1) reported successful regeneration of whole, fertile plants of Silene stenophylla Ledeb. from immature fruit tissue of Late Pleistocene age using in vitro tissue culture and clonal micropropagation. However, the plants in figures 2–4 in ref. 1 do not possess the diagnostic characters of S. stenophylla. The leaf morphology, inflorescence structure, floral morphology, indumentum, and seed characteristics instead all indicate that the plants belong to the Silene linnaeana Czerepanov (Lychnis sibirica L.) group. These taxa are only distantly related, sharing a most recent common ancestor many million years ago (e.g., 2, 3). Both taxa occur in rubble tundra in the area where the fossil fruit tissue was collected. S. stenophylla has a Far Eastern distribution, whereas the S. linnaeana group is widely distributed over Siberia (e.g., 4). By comparing morphological attributes as described in Floras available for the region (e.g., 4), one finds the following differences. The leaves of S. stenophylla are long and narrow and collected at the base, whereas those of the S. linnaeana group are narrowly lanceolate and occur on leafy stems. The inflorescence of S. stenophylla is a few-flowered thyrsoid, whereas the S. linnaeana group is characterized by a compound dichasium. The calyx of S. stenophylla is broad and inflated, whereas calyces in the S. linnaeana group are narrowly tubular to campanulate. Plants in the S. linnaeana group are pubescent, whereas S. stenophylla is glabrous, except on leaf margins of basal parts. In all these respects, the plants in figures 2 and 3 in ref. 1 are in agreement with the S. linnaeana group but not with S. stenophylla.

The seed morphology was studied in detail in a previous paper (5), where the original misidentification was probably made. We have compared seeds from specimens of the two groups and found, in agreement with, for example, Malyschev and Peschkova (4) that the seeds of S. stenophylla are about twice the size of those of the S. linnaeana group. Again, the seeds in figure 4 in ref. 1 are in agreement with those of the S. linnaeana group but not with S. stenophylla. Moreover, capsules in the S. linnaeana group often contain seeds of variable stages of maturity, as in figure 4 in ref. 1, and irregular morphologies (our own observations).

The regenerated plants possess diagnostic characters of S. linnaeana sensu stricto. These are linear petal lobes linear, numerous flowers, and short and dense inflorescent indumentum. The plant grown from seeds of an extant plant, however, has petals of triangular shape and rounded lobes, which is typical of Silene samojedora (Sambuk) Oxelman and Silene villosula (Trautv.) Petrovsky and Elven. Based on herbarium and literature records, the present distribution area for S. linnaeana s. str. covers much of South and Central Siberia, but not the Kolyma area, where, instead, S. samojedora occurs. This may indicate that the plant grown from extant seeds collected in the area and illustrated in figure 3A in ref. 1 belong to S. samojedora, but the information from the photograph and the lack of a comprehensive taxonomic revision of the group make a definite determination impossible.