Juncaceae Juss.

Balslev, H. (2009). Neotropical Juncaceae.

Morphology

Description

Perennial and usually rhizomatous or rarely annual herbs, glabrous or with hairy leaf margins. Rhizome creeping, ascending or erect , unbranched or branched, naked or covered by scales or splitting leaf bases. Culms erect , ascending or rarely procumbent , terete (rarely flattened, J. ensifolius Wikstr.), smooth or longitudinally ridged, naked or leaf bearing. Leaves linear or filiform , with an open and sometimes auriculate or closed sheath , spirally arranged or rarely distichous , blades sometimes reduced. Inflorescence terminal , sometimes pseudolateral, compound , cymose or racemose, usually in heads or spike -like clusters, rarely reduced to a single terminal or lateral flower . Flowers generally small, tepals <8mm long, perfect or imperfect, actinomorphic . Perianth segments 6 in 2 whorls of 3, glumaceous, equal or almost equal, free . Stamens 6 in 2 whorls of 3, opposite the perianth segments, inner whorl sometimes reduced; filaments filiform or somewhat flattened and widened at base; anthers oblong to linear , basifixed, obtuse or mucronate , dehiscing by 2 longitudinal lateral slits. Carpels 3, connate ; ovary superior , 1-locular, 3-septate or 3-locular; style 1, up to 10 mm long but usually shorter; stigmas 3, terete and of equal diameter throughout or sometimes tapering distally, twining with adaxial papillae; fruit an orbicular to oblong or ellipsoidal, 3- lobed , round or trigonous, loculicidal or circumscissile capsule . Seeds usully many per capsule , sometimes 3; outer seed coat hyaline , whitish or light brown, sometimes drawn out into tail-like appendages, often with distinct sculpturing; inner seed coat brown to castaneous or yellow.

General Description

Notes on delimitation

• The complete trimerous, pentacyclic flowers and the capsular fruit delimits Juncaceae morphologically from other glumiflorous families such as Poaceae and Cyperaceae and the grass-like habit and internal anatomy separates it from the related Thurniaceae.
• Molecular data suggest that Juncaceae and Cyperaceae are sister taxa and that together they are sister to Thurniaceae (Jones 2005).

Number of genera

Five:

• Distichia
• Juncus
• Luzula
• Oxychloe
• Patosia
• Rostkovia

Status

• Juncaceae are native in alpine meadows and in grasslands, especially in the highlands, where they may be weedy. Some are endemic to the Andes (all Distichia, Oxychloe, Patosia and species of Juncus and  Luzula), whereas other are widespread, often temperate species.

Distribution

Distribution in the Neotropics

• Distichia Nees & Meyen in the Andes from Colombia to northernn Chile/Argentina.
• Luzula DC. and Juncus L. mostly in the temperate zone and at high elevations in the tropical zone.
• Oxychloe Phil. in the Andes from Patagonia to Peru.
• Patosia Buchenau in the Andes from Bolivia to northern Chile/Argentina.
• Rostkovia Desv. in southernmost South America and Ecuador.

Diagnostic

Distinguishing characters (always present)

• Trimerous (very rarely dimerous), pentacyclic (rarely tetracyclic) flowers.
• Glumaceous tepals.
• Tricarpelate (very rarely bicarpelate) ovary.
• Capsule.
• 3 (Luzula) or more seeds.

Other important characters

• Grass-like.
• Smooth herbs.
• Without silica.

Key differences from similar families

Juncaceae are grass-like herbs with herbaceous culms, linear leaves, and usually many flowered inflorescences of small glumaceous flowers - just like Poaceae and Cyperaceae. Juncaceae differ from both these families in having:

• Smooth leaves and culms without silica encrustations.
• Complete whorls of 3+3 tepals.
• Usually 3+3 stamens.
• Gynoecium of 3 carpels.
• Fruit with at least 3 seeds and usually many more.

Useful tips for generic identification

• Distichia - cushion forming, leaves distichous, flowers unisexual.
• Juncus
- grass-like, smooth, many-flowered culms, many seeded capsules.
• Luzula - grass-like, hairy leaf margins, many-flowered culms, 3-seeded capsules.
• Oxychloe - cushion forming, leaves prickly, flowers with two bracteoles.
• Patosia -  cushion forming, leaf margin finely serrate, flowers with one bracteole.
• Rostkovia
- grass-like, single-flowered culms, capsule orbicular and many seeded.

Literature

Important literature

Balslev, H. 1996. Juncaceae. Flora Neotropica Monograph 68: 1-168.

Jones, E. et al. 2005 The Juncaceae-Cyperaceae interface: a combined plastid gene analysis. In J. T. Columbus et al. (eds). Monocots: Comparative Biology and Evolution, 2 vols. Rancho Santa Ana Botanic Garden, Claremont, CA.

Kirschner, J. et al. 2002. Juncaceae 1: Roskovia to Luzula, Species Plantarum: Flora of the World Part 6: 1-237.

Kirschner, J. et al. 2002. Juncaceae 1: Juncus subg. Juncus, Species Plantarum: Flora of the World Part 7: 1-336.

Kirschner, J. et al. 2002. Juncaceae 1: Juncus subg. Agathryon, Species Plantarum: Flora of the World Part 8: 1-192.

Juncaceae, Susan Carter. Flora of Tropical East Africa. 1966

Morphology General Habit

Annual or perennial herbs, rarely shrubs

Morphology Roots

Roots fibrous

Morphology Stem

Stems erect, cylindric or rarely compressed, naked or leafy, sometimes rhizomatous or stoloniferous, and then horizontal or ascending

Morphology Leaves

Leaves grass-like or cylindric, sheathing at the base, sometimes reduced to cataphylls; sheaths open and sometimes auriculate, or closed

Morphology Reproductive morphology Inflorescences

Inflorescence terminal, often pseudo-lateral, compound or rarely simple with one flower, umbellate, paniculate, the flowers solitary or in capitula (heads); bracts leaf-like, scarious or membranous, persistent; bracteoles sometimes present

Morphology Reproductive morphology Flowers

Flowers small, regular, hermaphrodite; rarely the plants dioecious

Morphology Reproductive morphology Flowers Perianth

Perianth-segments 6, in two series, subequal, glumaceous, green or brown, usually membranous at the edges

Morphology Reproductive morphology Flowers Androecium

Stamens 6, opposite and shorter than the perianth-segments, the 3 inner sometimes absent; filaments linear or triangular; anthers basifixed, 2-thecous, introrse, dehiscing longitudinally

Morphology Reproductive morphology Flowers Gynoecium

Carpels 3, joined; ovary superior, 1- or 3-locular; style rarely absent; stigmas 3

Morphology Reproductive morphology Fruits

Fruit a loculicidal capsule

Morphology Reproductive morphology Seeds

Seeds 3 or many, ovoid to obovoid, apex sometimes apiculate, base sometimes tailed