Eriocaulaceae Overview

Eriocaulaceae are easily distinguished from other monocot families because most species have short stems, leaves in a rosette, long scapes with small unisexual flowers grouped in dense heads (capitula), a 3 or 2-locular ovary with a single pendulous ovule per locule and spiraperturate pollen grains.

Some species are of considerable economic importance in Brazil, especially in the genera Syngonanthus and Comanthera. The plants are collected when in flower, dried locally in the sun, and sold on as ornamental objects. They are often exported to various countries as “everlasting plants”. Some species such as Comanthera elegans have been traded at the rate of 40,000 kg/year and some, like C. magnifica and C. mucugensis, are critically endangered due to over-exploitation. At the present time the scapes of Syngonanthus nitens, under the popular name of “golden grass”, are widely commercialized and used for the production of a diversity of local handcrafts. In the regions where these plants occur naturally, they are one of the main sources of income for local inhabitants, especially in the ‘campos rupestres’ vegetation of the Espinhaço mountain range (States of Minas Gerais and Bahia, Brazil) and Serra Geral (State of Goiás, Brazil) and in the cerrado around Jalapão (State of Tocantins, Brazil) and in western Bahia. Because of the economic importance of Eriocaulaceae, and the discovery that several economically valuable species are threatened with extinction, a National Conservation Plan was drawn up by the Brazilian Ministry of the Environment (PAN Eriocaulaceae) which established  priority for conservation activities.

Eriocaulaceae are a sub- to pantropical family, including around 1400 species. The biggest genera are Eriocaulon (ca. 400-800 species), which occurs on five continents, Paepalanthus  (ca. 700 species) and Syngonanthus (ca. 130 species), both with a disjunct occurrence between Americas and Africa. Mesanthemum is restricted to the African continent and Lachocaulon to North America. All other genera (Actinocephalus, Comanthera, Leiothrix, Rondonanthus and Tonina) are endemic to South America. Two centers of diversity are recognized, in the Guayana Shield and in southeastern Brazil, in the Espinhaço Mountain Range, especially on quartzitic ‘campos rupestres’ (high altitude rocky savannas). The Espinhaço Range is the most species-rich are, wich ca. 700 species. 

Judd et al. (2002) and APG II 2003 include Eriocaulaceae within Poales, but the family was placed previously in its own order Eriocaulales (Cronquist 1981), within the Commeliniflorae (Dahlgren et al. 1985) or in the Commelinales (Judd et al. 1999). The family is morphologically well-delimited and has been shown to be monophyletic, although inter- and infrageneric relationships are still not well resolved. 

Xyridaceae is the putative sister family to Eriocaulaceae, sharing morphological characters, habitat and adaptive strategies. Abolboda shares unique characters with Paepalanthoideae, including a gynoecium with lateral stigmas and apical nectariferous appendices. The relationship between these families needs better investigation, in the search for morphological synapomorphies. In this context, the e-monocot project will promote integration of knowledge on their evolution, as a pioneer common approach.

The last full revision of Eriocaulaceae was made by Ruhland (1903), who established the taxonomic basis of the family which is still in use. This author recognized about 560 species and two subfamilies: Eriocauloideae with diplostemonous flowers and glandular petals including Eriocaulon and Mesanthemum; and Paepalanthoideae with isostemonous flowers and eglandular petals, including: Paepalanthus, Tonina, Lachnocaulon, Philodice, Syngonanthus, Blastocaulon, and Leiothrix. Since then more than twice the original number of species have been described and six new genera have been proposed: Actinocephalus, Carptotepala, Comanthera, Moldenkeanthus, Rondonanthus and Wurdackia. Three of them are already considered to be synonymous to existing genera: Moldenkeanthus in Paepalanthus, Wurdackia in Rondonanthus, and Carptotepala in Comanthera. Recently, based on morphological and molecular studies Blastocaulon was  synonymized with Paepalanthus and Philodice with Syngonanthus. Currently the genera accepted in Eriocaulaceae are: Actinocephalus, Comanthera, Lachnocaulon, Leiothrix, Paepalanthus, Rondonanthus, Syngonanthus and Tonina in Paepalanthoideae and Eriocaulon and Mesanthemum in Eriocauloideae. The traditional circumscription of genera in Eriocaulaceae has been based primarily on a few floral characters, including: a) the degree of petal union in pistillate flowers; b) the presence of glands on petals; c) the number of stamens per flower; and d) the number of pollen-sacs per anther.

Recent studies involving researchers worldwide and using morphology, anatomy, floristics, taxonomy, chemistry, population biology, genetics, economic botany, physiology, karyology and molecular phylogenetics have provided new data for understanding the family. These studies have also shown that apart from the characters used by Ruhland, vegetative and floral parts also display many other characters, principally relating to the form and anatomy of floral structures, embryology, hair type, architecture, seed testa and apertures and sculpturing of the pollen grains.

Research trends nowadays should concentrate on phylogenetic analyses with a  wider sample of extra-Brazilian species, notably those from the Guiana Shield, Africa and Asia. Floral biology and population genetics remain poorly understood, including pollination and dispersal mechanisms. The ecological and reproductive factors favoring micro-endemism also deserve special attention. In this context e-taxonomy and the eMonocot project could be a powerful tool to coordinate and integrate future research strategies. 

Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith