Juncaceae
The Juncaceae (scientific name Juncaceae) form a family of grass-like monocotyledonous plants, with linear leaves that have a sheath and blade but no ligule, inflorescences normally condensed in terminal glomeruli and differ from grasses because the flowers have obvious tepals, the leaves are tristic, and the fruits are capsules. They have colonized all environments, especially those in temperate zones, and are pollinated by wind.
The family name was used in modern classification systems such as the APG III classification system (2009) and the APWeb (2001 onwards) in which it is assigned to the sedge-sedge clade of the order Poales. In the family are the rushes and the like. The economic importance is limited, some are used as ornamentals, some used to weave baskets or chairs.
Description
- Theoretical Introduction in Descriptive Terminology of Plants
Habit: Herbs, perennial (rarely annual), without silica bodies, when perennial their stems are usually rhizomatous, round and solid.
Alternate, spiral leaves, usually tristicus (rarely distichus), bifacial or unifacial (more or less rounded, not recognizing two sides), basal or along the lowest portion of the stem, thin, composed of a sheath (sheathing leaves) and lamina, the sheath usually open, the lamina simple, undivided, with entire margin, with parallel, linear, flat or cylindrical venation. Usually with auricles. With or without ligule. No stipules.
Inflorescences basically determined, terminal, very branched, but usually condensed in a glomerulus, or they can also have solitary flowers, or composed of 1-many cymes.
Flowers usually hermaphroditic, but occasionally unisexual (then dioecious plants), inconspicuous, regular, bracteate, hypogynous.
6 tepals arranged in 2 whorls (rarely 3 in 1 whorl, or 4 in 2 whorls), separate, imbricate, usually green, red-brown, or black, but sometimes white or yellowish, scarious (thin and like scales), without hypanthus. The outer and inner tepals are separate.
Androecium with 6 stamens in 2 whorls (or sometimes 3 stamens in 1 whorl, or 4 in 2 whorls), let's diplost when in 2 whorls (the outer whorl opposite the outer tepals and the inner one opposite the inner tepals), filaments separated from each other and from the tepals. Basifix anthers, longitudinal dehiscence.
Pollen monoporous, in obvious tetrads.
Superior gynoecium, tricarpellate, carpels connate, 3 or 1 locule, with axillary or parietal (occasionally basal) placentation, style usually 3-branched, 3 stigmas usually elongated, sometimes twisted. ovules numerous (rarely 3 or 1), anatropous, bitegmic.
There are no nectaries.
The fruit is a loculicidal capsule (rarely indehiscent).
3 to numerous seeds, with starchy endosperm.
Ecology
Cosmopolitan family, mostly from temperate and montane regions. Often in moist habitats, but there are notable exceptions, such as Juncus trifidus.
The inconspicuous flowers of the Juncaceae are predominantly wind-pollinated, interbreeding is commonly favored by protandry (on the same plant the male flowers mature earlier), but some species are self-pollinated. There may also be species pollinated by insects.
The dispersal of the small seeds is produced by the wind, water, or they can also be transported by animals externally (without consuming them).
Phylogeny
- Theoretical Introduction in Philogenia
The monophyly of Juncaceae is supported by ITS sequences (Kristiansen et al. 2005, Roalson 2005), and by analysis of a combination of genes (Jones et al. 2007). The monophyly of Juncaceae was not clear until recently, although it was already known that Prionium (now in Thurniaceae) should be excluded from it. Two studies found that Juncaceae was not monophyletic, as Oxychloe was found to be embedded in Cyperaceae, or sister to the rest of Cyperaceae, by Plunkett et al. 1995, and Muasya et al. 1998. According to Soltis et al. (2005), what must have happened in the analyzes of Plunkett et al. (1995) and Muasya et al. (1998), is that the former may have used a collection of leaves that was a mix of Oxychloe with a sedge, and almost surely they sequenced the sedge, while in the latter the sample must have been contaminated.
It is not clear which characters in the family are synapomorphic, many are generalized characters in monocots.
Juncaceae, Cyperaceae and Thurniaceae share two characters that may be synapomorphies: tristic leaves and tetrad pollen. The 3 families form the sedge-sedge clade, see Poales for a discussion of this clade.
Recent phylogenetic analyzes (Drábková et al. 2003, Roalson 2005) indicate that Juncus is not monophyletic, Luzula sprang from it > and a group of Andean plants (Oxychloë and Disticia). The fact that Juncus is glabrous suggests that this condition may be a synapomorphy of the family (even if it were homoplastic).
Many members of this family appear superficially grass-like, but the tristic leaves, flowers with obvious tepals, and capsular fruits make the distinction clear. In some Juncus species, the long bract below the inflorescence is upturned to appear to be a continuation of the stem, and the inflorescence appears lateral.
Taxonomy
- Theoretical Introduction in Taxonomy
The family was recognized by the APG III (2009), the Linear APG III (2009) assigned it the family number 98. The family had already been recognized by the APG II (2003).
6 genera, about 400 species. The most represented genera are Juncus (300 species) and Luzula (80 species).
List of genera and their synonyms, according to APWeb (accessed January 2009):
- Andesia Hauman = Oxychloe Phil.
- Distichia Nees " Meyen
- Ebingeria Chrtek & Krisa = Light DC.
- Juncus L.
- Light DC.
- Marsippospermum Desv.
- Microschoenus C.B.Clarke = Juncus L.
- Oxychloe Phil.
- Patosia Buchenau = Oxychloe Phil.
- Rostkovia Desv.
Prionium now belongs to Thurniaceae.
Economic importance
The economic importance is limited.
Juncus effusus and J. squarrosus are used to make baskets and chairs.
A few species of Juncus and Luzula are used as ornamentals.
Disticia is used in Peru as fuel and a substitute for peat moss Sphagnum to prepare mixes of plant substrates.