Xyridaceae Overview

The Xyridaceae are distingushed from the other families of Monocotyledons by a set of vegetative and reproductive characters. The leaves are usually rosulate and the stem rhizomatous with short internodes. The inflorescence is scapose (Xyris), and pedunculate to almost sessile in the other genera. Xyris and Abolboda are distinguished by their spikes, which have imbricate, usually coriaceous bracts, with few to numerous flowers. The flowers are actinomorphic or zygomorphic, trimerous, with a distinct calyx and corolla. In Xyris  and Abolboda the lateral sepals are navicular, forming a zygomorphic calyx. In Xyris the anterior sepal is distinct and usually membranaceous and caducous, but in Abolboda it is much smaller or absent. In the other genera the calyx is actinomorphic. The corolla is usually yellow (Achlyphila, Orectanthe and Xyris ), purplish blue or white (Abolboda) and white or magenta  (Aratitiyopea). In Xyris and rarely in Abolboda there is a second whorl in the androecium consisting of staminodes. The staminodes in Xyris are plumose.

The ovary is superior and the gynoecium has appendages in Abolboda, Aratitiyopea, and Orectanthe; the stylar branches can be long to short. There is a wide range of variation in placentation types, an important diagnostic character both for distinguishing genera and for dividing Xyris into subgenera.

Some Xyris species native to Brazil are economically important and are included in the “everlasting plant” trade along with species from other families, particularly the Eriocaulaceae. These plants occur in the campo rupestre vegetation of the Espinhaço mountain range in the states of Minas Gerais and Bahia and in the Serra Geral in the states of the central west of Brazil (e.g. Goiás).  They are known are dried flowers of the cerrado and are commercialized as flower arrangements for interior decoration. The sale of the inflorescences is an important source of income for local communities in the regions where these species occur.

Xyris species inhabit acid, oligotrophic  soils which are seasonally or permanently water-logged and very low in nutrients. Some species of the cerrado and campo rupestre have adaptations against fire and water stress in the form of robust rhizomes protected by leaf sheaths which are able to rapidly produce new vegetative shoots in favourable conditions.

Mon, 2012-11-12 20:19 -- Anonymous (not verified)
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith