Linaceae

Description

Lianas, trees, shrubs, or herbs. Tufted hairs absent. Leaves spirally or distichously arranged. Stipules lateral. Flowers hypogynous. Petals caducous, contorted. Fruit a drupe or a capsule (sometimes with indéhiscent mericarps). Seed not persistent, with slightly or not developed arillode.

Morphology

Linaceae sensu stricto are distinguished by several flower characters from the other two families, viz. disk absent or almost so, filaments connate at base, styles 3-5, and arillode absent or hardly developed. The distinction of these families is also sustained by wood and anatomical research (HEIMSCH & TSCHABOLD, 1972) and pollen morphological studies (SAAD, 1962; OLTMANN, 1971). NARAYANA & RAO (1978) concluded that on the basis of floral morphology and embryology Linaceae are related to Erythroxylaceae and Humiriaceae, in addition to showing affinity with Ctenolophonaceae and Ixonanthaceae. In his studies on seeds, CORNER (1976) opposed an affinity with Geraniaceae, but suggested Malpighiaceae and possibly also Oxalidaceae as closer relatives.

Within Linaceae sensu stricto there are two distinct subfamilies, Linoideae and Hugonioideae. They can be distinguished as follows:
  1. Linoideae — Erect herbs or small shrubs. Petals usually long-clawed. Stamens as many as petals, alternating with the same number of staminodes. Ovary 6-10-celled. Fruit usually a capsule. — Almost entirely confined to the northern hemisphere.
  2. Hugonioideae — Trees or lianas with hooks, rarely shrubs, all ligneous. Petals not or hardly clawed. Stamens twice as many as petals. Ovary 3-5-celled. Fruit a drupe, rarely splitting finally in indéhiscent mericarps. — Pantropical, but hardly on the northern hemisphere except in southern Southeast Asia.


In Malesia only Hugonioideae occur, and have not seldom been distinguished as a separate family Hugoniaceae (e.g. by EXELL & MENDONÇA, 1951; TAKHTAJAN, 1969; DAHLGREN, 1975; CRONQUIST, 1981). CORNER (l.c.) dwelt extensively on the anatomical structure of their seeds. In his opinion the simple tegmen of the Linoideae may be derived from the mesotestal construction in the Hugonioideae. The genus Indorouchera of the Hugonioideae may yield the most primitive pollen type in Linaceae.

Taxonomy

In this work Linaceae sensu lato have been split into three families: Linaceae, Ixonanthaceae and Ctenolophonaceae, among which the latter deviates most.

In order to elucidate distinction of the two segregated families of Linaceae sensu lato VAN HOOREN & NOOTEBOOM () prepared the following diagnoses:
  • Linaceae — Lianas, trees, shrubs, or herbs. Tufted hairs absent. Stipules lateral. Leaves spirally or distichously arranged. Flowers hypogynous. Petals caducous, contorted. Disk absent (or traces of an extrastaminal disk present, l.c. 556 sub Philbornea). Filaments basally connate in a tube. Styles 3-5(-6), simple. Fruit a drupe or a capsule (sometimes with indéhiscent mericarps). Seed not persistent, with slightly or not developed arillode. — Stomata paracytic.
  • Ixonanthaceae — Trees. Tufted hairs absent. Stipules lateral. Leaves spirally arranged. Flowers perigynous. Petals persistent in fruit, imbricate (extra-Mal. also contorted). Disk intrastaminal. Filaments free, inserted outside and against the disk. Style 1, simple. Fruit a capsule. Seed not persistent, with an obvious basal wing or suprahilar arillode. — Stomata paracytic.
  • Ctenolophonaceae — Trees. Tufted hairs present. Stipules interpetiolar. Leaves opposite. Flowers hypogynous. Petals caducous, contorted. Disk extrastaminal. Filaments free, inserted halfway on inside of disk. Style 1, apically bifurcate, with 2 stigmas. Fruit a capsule. Seed persistent on the columella after the valves have been shed, with hairy-papillose arillode. — Stomata anomocytic.

Synonymy

Linaceae