Notes on Dryopteris expansa

Dryopteris expansa (C.Presl) Fraser-Jenk. & Jermy var. pseudospinulosa (Rosend.) (Finland, Lammi, Lampelto, 1992). – Image: Harri Harmaja (scanned from dried specimen). – This morph has small, dull pale green leaves with small, almost uniformly coloured petiole scales. I have seen specimens collected throughout the country, occurring sympatric with var. expansa, though the morph has been considered as a northern one. The morph may deserve to be recognized at some taxonomic level though it is generally not assigned taxonomic relevance (Widén, C.-J, Sarvela, J. & Ahti, T. 1967: The Dryopteris spinulosa complex in Finland. – Acta Bot. Fennica 77: 1-24.). (Quite near to the depicted plant I have found a small stand of D. dilatata s. str.; in Finland, the occurrence is farthest inland of this suboceanic species.)
    The morphological variability of D. expansa in Europe is well-known, and has also been noted by me in Finland. The chemistry, too, is unusually variable (Widén, C.-J. 1969: Chemotaxonomic investigations on Finnish Dryopteris species and related North American taxa. – Ann. Acad. Sci. Fennicae, ser. A IV Biologica 143: 1-19.). The species as conceived currently may actually consist a few cryptic species.

The southern Finnish plants display following variation according to my observations:

• Size of plants grown in similar conditions.

• Consistency of the dried plant. – Some plants possess a rather fragile petiole and rachis in the dried condition. Even though this property appears vague,  it may represent interesting genetic variability; this kind of plants probably also share sparsely glandular upper surface of lamina and an utmost faint agreeable scent of both fresh and dry leaves.

• Presence of the dark stripe in the petiole scales. – It may be is absent, excepting the scales at the very base close to the rhizome.

• Intensity of the green colour of the leaf lamina.
• Shape of leaf lamina.
• Degree to which the leaf lamina is dissected.

• Shape of the lowest pinna; this character largely depends on the size of its first basiscopic pinnule as compared with that of the second one.

• Presence and amount of glandular hairs in all parts of the leaf, including the indusia. – E. g., the plants can fairly sharply be divided into two groups: in the most common morph the glands only occur on the underside of the lamina while some plants have them on both surfaces (the lamina of some of the latter plants may even be slightly viscid in humid weather!).

• Odour of the apical portion of a fresh, young, expanding leaf, as observed without any crushing. – Most plants only possess an inconspicuous smell of fresh plant tissue but sometimes I have observed a faint, very agreeable scent being emitted. This odour somewhat resembles that of the flowers of Viola mirabilis L. and V. selkirkii Pursh ex Goldie. Apparently all these scenting plants are glandular on the upper side of lamina. The chemical compounds responsible for the scent may be at least partly the same which are present in the essential oil of the well-known fragrant species of Dryopteris, D. fragrans (L.) Schott. Also some other species of the genus are known to possess a distinctive odour to the fresh fronds, but none has been reported in D. expansa.

• Size and colour of the sori; the latter are larger and appear blackish when the number of well-developed sporangia is great.