Linaceae (Flax Family)

Above: Linum bienne (Pale Flax or Narrow-leaved Flax) - flowers about 2 cm diameter

Linum bienne (Linum angustifolium) is an annual or perennial found on dry banks and field borders. There may be a very short rootstock and there are few stems which are wiry and more-or-less erect and slightly branching with spreading ascending branches. This species is found in Macaronesia, Western Europe, the Mediterranean and Iran (see: http://powo.science.kew.org/taxon/544373-1).

Linum bienne is similar to Linum usitatissimum (Common Flax) and the two can be hard to distinguish. The latter is a cultivated form introduced into the British Isles (Flax is grown for fiber for making linen and for linseed oil). In bienne the leaves have 1-3 veins, whilst those have usitatissimum have 3. The leaves of bienne are also narrower (0.5 to 1.5 mm in width) versus 1.5 to 3(4) mm in usitatissimum. We can not see the detail of the leaves, which are alternate, in the above photograph, but the flowers do show differences. In bienne the petals are often barely touching, but in contact with their neighbours in usistatissimum. In bienne the petals are usually a very pale lilac-blue but in usiatissimum they are a dull purple-blue. Linum usitatissimum also has stouter stems, up to 60 cm tall. Thus, I have determined this specimen as Linum bienne (though a close examination of the leaves would have confirmed this).

Additionally, the inner partitions between the valves of the fruit capsule are smooth in usitatissimum and downy in bienne. The sepals occur in two whorls: 3 inner sepals and 2 outer in both species and the 3 inner are broader with a broad membranous margin fringed with cilia whilst the 2 inner are narrower with with narrow entire membranous margins. The difference is said to be less pronounced in usitatissimum. However, there seems to be some confusion in the literature regarding sepal characters with those of bienne described as pointed and those of usitatissimum as blunt; whereas other sources describe them as acuminate (tapering to a sharp point) in both species (especially the outer sepals with the inner sepals being blunt in bienne). I would not want to commit without examining many specimens.

The family Linaceae consists of herbs, subshrubs, shrubs, trees and lianas. The flowers usually have 5 sepals and 5 petals (occasionally 4). The filaments of the 5 stamens are fused together at their bases to form a ring or tube. A nectary develops as a gland (protuberance) on the outside of each stamen filament base. The nectaries develop stomata, presumable for nectar secretion.

The ovary of Linum is divided into 5 compartments, each containing 2 ovules. The nectaries are very small. There are 5 styles (sometimes 3) that are more or less free and not fused together. The fruit is a globose capsule that splits into 10 valves (cocca), each containing one seed.

Above: Linum catharticum (Fairy Flax or Purging Flax) was once used as a purgative. It occurs from Europe, to western Siberia, Iran and Morocco (http://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:544405-1). It occurs on pastures and abnks. The wiry stems are curved at the base but otherwise upright and reach 30 cm in height. The stems produce ascending and spreading branches. Unlike the previous species, the leaves are distinctly arranged in opposite pairs (except the uppermost pair which are often alternate). The leaves are narrow, elliptcal and about 2 cm in length and become narrower towards the shoot apex. The bracts are leaf-like but smaller than the leaves.

The fruit of Fairy Flax is a globular capsule enclosed by the sepals and splitting into 10 valves. Note the 'yellow eye' due to yellow pigment on the petal bases, which probably functions to attract pollinators by mimicing pollen. The flowers are only about 6 mm in diameter. The petals are about twice as long as the sepals.

An additional feature of the genus Linum is the presence of 5 'staminodes'. The stamens alternate with the petals and 5 'staminodes' lie opposite the petals. However, these staminodes are possibly stamen appendages rather than undeveloped stamens (see: https://bsapubs.onlinelibrary.wiley.com/doi/pdf/10.3732/ajb.1000431)

Further reading

Nectary and staminodes: Schewe, L.C., Sawhney, V.K. and Davis, A.R. 2011. Ontogeny of floral organs in flax (Linum usitatissimum; Linaceae). American J. Bot. 98(7): 1077-1085. https://bsapubs.onlinelibrary.wiley.com/doi/pdf/10.3732/ajb.1000431