Botanic Garden Meise

 Research

Monographic and systematic studies in Rubiaceae

Contact: E. Robbrecht

Other researchers: P. De Block, S. Dessein, P. Stoffelen

How many Rubiaceae are there and where to find them?

  • Asteraceae: 21 000 spp.
  • Orchidaceae: 17 500 spp.
  • Leguminosae: 16 500 spp.
  • Rubiaceae: 13 000 spp.
  • Graminae: 8 000 spp.
  • Mammalia: 5 000 spp.

 

The Rubiaceae are the fourth largest family of flowering plants after the Asteraceae, Orchidaceae and Fabaceae (sensu lato, = Leguminosae) and total circa 650 genera and 13,000 species. In temperate regions, the Rubiaceae are represented by only a few herbaceous genera, e.g. Galium and Asperula. They possess very small flowers and leaves arranged in whorls (actually, the whorls are formed by a leaf pair and leaf like structures of stipular origin of the same node). The bulk of the family is tropical and predominantly woody. The Rubiaceae constitute an important component of all tropical woody vegetation, especially the rain forest understory.

How to recognize them?

Most Rubiaceae are shrubs or small to large trees. They are easily recognized at family level by decussate, entire leaves, presence of stipules, actinomorphic flowers and an inferior ovary.

Some well-known and economically important Rubiaceae

The Rubiaceae's best-known member is undoubtedly Coffea. As a major economic crop the coffee plant is now cultivated throughout the tropics. Other economically important species are e.g. Cinchona, which yields quinine, used as a cure for malaria, and Psychotria ipecacuanha, which yields ipecac, widely known as an emetic. Many more species are used by various indigenous people as medicinal plants. Detailed study of the large range of alkaloids the Rubiaceae possess might lead to the development of new drugs.

The Rubiaceae family is also important in horticulture. Many genera, such as Gardenia, Ixora, Pentas, Mussaenda and Sherardia, are well known ornamentals.

The Rubiaceae's best-known member: Coffea

Morphological and biological variation

The morphological and biological variation displayed by the Rubiaceae is very large. Some examples:

Asperula odorata Crucksanksia hymenocodon Pygmaeothamnus species Posoqueria longiflora
Asperula odorata, an temperate herbaceous Rubiaceae with leaves arranged in pseudowhorls (whorls formed by a leaf pair and leaflike structures of stipular origin of the same node). Herbaceous Rubiaceae also occur in the tropics. Crucksanksia hymenocodon is an example from the deserts of Chili. This Pygmaeothamnus species is a geofrutescent from Africa. Geofrutices or geoxylic plants are characterized by massive woody underground stems and occur in dry open areas, often ravaged by fires. Posoqueria longiflora is a neotropical species with large white flowers. The long and narrow corolla tubes and the white colour of the flowers are an indication that this species is pollinated by hawk-moths.
Aida micrantha Breonia havilandiana Pentas Psychotria granvillei
This picture of Aida micrantha clearly shows a mass of yellow pollen on the stigma. This is the result of the reproductive strategy known as secondary pollen presentation. While the flower is still in bud stage, pollen is shed from the anthers onto a pollen presenter, in the case of Aidia the stigma. At anthesis the pollen presenter is exposed, thereby presenting pollen to the pollinators. Breonia havilandiana, a tree species from Madagascar, shows strongly congested head-like inflorescences. The aggregation of the flowers into a compact structure makes the inflorescences more attractive to pollinators. This species of Pentas from Madagascar heightens the attraction of its inflorescences to pollinators by the presence of floral semaphylls. One of the calyx lobes of every flower is enlarged, showy, leaf-like and white in colour. This neotropical Psychotria species of the Cephaelis group possesses a highly condensed involucrate inflorescence. The involucre is coloured a brilliant red and helps the plant to attract pollinators. In fruit stage, the red involucre contrasts strongly with the blue berries, attracting dispersers.

How well do we know Rubiaceae?

Until recently, the Rubiaceae were not as extensively studied as other families. This was partially due to the size of the family and to its reputation as being "difficult", with many large and ill-defined genera. More recently however, the Rubiaceae have become the focus of detailed studies. International conferences are now organized to provide a contact platform for Rubiaceae specialists (1993, Missouri Botanical Garden, St. Louis, U.S.A.; 1995, National Botanic Garden of Belgium, Meise, Belgium).

Links to some Rubiaceae specialists and Rubiaceae sites

Rubiaceae sites:

Some Rubiaceae specialists:

Eighty years of Rubiaceae research at the Garden.

In our institute systematic studies on tropical Rubiaceae have been carried out continuously for almost eighty years. This has resulted in the description of many new species, in the production of revisions and monographs based on classical herbarium taxonomy and in detailed character analysis in fields such as palynology, floral biology, etc. Many publications on Rubiaceae have been produced by BR researchers. The following botanists played an important historical role in the Rubiaceae research at the Botanic Garden.

Members of the current Rubiaceae Research group are:

Collaboration between the BR Rubiaceae research group and researchers from other institutes is extensive.

Current research and projects

The large species number and the great morphological, anatomical and biological variation make the Rubiaceae a very interesting family to study. Our research ranges from monographs based on classical herbarium taxonomy to in-depth morphological, anatomical and palynological studies. In the near future molecular research will be started. Although our interest extends to all Rubiaceae worldwide, we currently focus our attention on certain tribes and certain geographic areas.

To help us with our Rubiaceae research we are assembling a large collection of living Rubiaceae. Our ultimate aim is to have living representatives of all Rubiaceae genera.

We further collect as much Rubiaceae literature as we can find. Recently, an Endnote database was started.

Tribes studied by BR Rubiaceae team

- Pavetteae

The Pavetteae comprise 17 genera and circa 800 species, all of which are woody. The tribe is paleotropical. Important genera are e.g. Pavetta (400 spp.) and Tarenna (200 spp.). Currently, research is focused on the genus Tarenna and on the Malagasy representatives of the tribe.

  • monographic study of Tarenna in continental Africa and Madagascar
  • revision of the Malagasy endemics Homollea, Homolliella, Schizenterospermum
  • revision of the Afro-malagasy genera Paracephaelis and Coptosperma (Enterospermum)
  • description of the new genera Robbrechtia and Helictosperma, endemic to Madagascar

- Ixoreae

There are circa 400 species in the pantropical genus Ixora, which is the largest representative of this tribe. Our research is focused on the African species of this genus.

  • revision of the continental African species of Ixora (Opera Bot. Belg. 9)
  • revision of the Malagasy species of Ixora

Two other tribes are studied in collaboration with researchers of the Catholic University of Leuven, K.U.L., notably

- Spermacoceae: Dessein S.:

- Psychotrieae: Piesschaert F.:

Geographic areas of high interest to the BR Rubiaceae team

-Central Africa

Our interest in this area is a result of our colonial history and of the fact that BR publishes the Flore d'Afrique Centrale. The lowland rain forests of Cameroon, Gabon, Congo-Brazzaville and Congo-Kinshasa are renowned for their biological richness. Rubiaceae form a large component of the understory of these forests. The region also encompasses mangrove forests, savanna woodland, montane forest and other vegetation types, the diversity of which results in high species diversity. Eventually, we hope to produce a flora treatment of the Rubiaceae of Central Africa.

-Madagascar a biological treasure island threatened with destruction

As a result of its long-time separation from Africa, Madagascar's flora and fauna are unique. Circa 12,000 plant species occur, an amazing 80% of which are endemic. However, most of the original vegetation on the island has already been destroyed. What remains is under serious threat and Madagascar is now generally considered as the world's most threatened natural area.

In Madagascar, the Rubiaceae is the second largest family of flowering plants, represented by circa 1000 species. They occur in all vegetation types, but are especially common in the understory of the humid evergreen forests on the East Coast of the island. The Rubiaceae are systematically very poorly known and no flora treatment exists. Although easy to recognize at family level, they are more difficult to identify to generic, let alone, specific level.

Collaboration

  • Prof. Dr. Christian Puff (Institute of Botany, University of Vienna; http://mailbox.univie.ac.at/~puffc9 )
  • Wood anatomy: Dr. S. Jansen (KUL) The interfamilial relationships of the Rubiaceae are studied on the basis of wood anatomical characters. The morphology of vestured pits is studied in detail. Another feature of interest is aluminium accumulation in wood and leaves within the Rubiaceae in order to determine the taxonomic significance of this character.
  • Palynology: Dr. S. Huysmans (KUL) The taxonomic importance of pollen morphological characters in the Rubiaceae is considerable. Pollen has been studied in detail for the subfamily Cinchonoideae. The distribution and nature of orbicles is studied within the whole family. Furthermore, ontogenetical study of Rubiaceae pollen, orbicules and tapetum is undertaken.
  • The Psychotrieae: Dr. F. Piesschaert (KUL)The Psychotrieae is the largest tribe within the Rubiaceae (± 2000 species). Because of its size and the little variation in flower morphology, the generic delimitation of this tribe remains one of the major problems in Rubiaceae systematics. In this project, fruit characters (morphological and anatomical variations of pyrenes and seeds), and pollen morphological characters are studied in non-African Psychotrieae, in order to propose a global generic delimitation of the tribe.
  • The Spermacoceae sensu lato: Drs. S. Dessein (KUL) This large tribe comprises the former tribes Hedyotideae, Knoxieae and Spermacoceae sensu stricto. The delimitation at tribal level remains problematic and there are still numerous taxonomic problems within the Spermacoceae sensu lato. These can be solved only with a multidisciplinary study. Morphological and anatomical characters, especially pollen and seed morphology, of the tribe are studied. A molecular study will be carried out in order to clarify phylogenetic relationships within the tribe and provide an evolutionary framework to discuss the morphological variation observed in the Spermacoceae sensu lato.
  • Revision of Pauridiantha: Drs. S. Ntore (KUL and Univ. of Bujumbura) Pauridiantha is a genus of the African mainland with one representative in Madagascar. It consists of circa 40 species. Its delimitation and that of the closely related satellite genera Commitheca, Poecilocalyx, Rhipidantha and Stelechantha is still a matter of dispute. This study aims to complete a revision of Pauridiantha. Anatomical (including seed, wood, and ovary anatomy), pollen morphological and chorological characters will be used in the delimitation of species.

Key publications

  • De Block P. (1998) The African species of Ixora (Rubiaceae - Pavetteae). Opera Bot. Belg. 9: 1-217.

  • De Block P. (1998) Rubiaceae. Distr. Pl. Afr. 43: 1421-1470.
  • De Block P. & Robbrecht E. (1997) On the ovary structure of Dictyandra and Leptactina compared with other Pavetteae (Rubiaceae - Ixoroideae), or evolution from multiovulate to uniovulate placentas. Bot. Jahrb. Syst. 119: 99-113.
  • Huysmans S., Robbrecht E. & Smets E. (1998) A collapsed tribe revisited: pollen morphology of the Isertieae (Cinchonoideae-Rubiaceae). Rev. Palaebot. Palynol. 104: 85-113.
  • Jansen S., Robbrecht E., Beeckman H. & Smets E. (1997) Wood anatomy of predominantly African representatives of the tribe Psychotrieae (Rubiaceae - Rubioideae) . IAWA J. 18: 169-196.
  • Jansen S., Dessein S., Piesschaert F., Robbrecht E. & Smets E. (2000) Aluminium accumulation in leaves of Rubiaceae: Systematic and phylogenetic implications. Ann. Bot. 85: 91-101.
  • Piesschaert F., Robbrecht E. & Smets, E. (1997) Dialypetalanthus fuscescens Kuhlm. (Dialypetalanthaceae): the problematic taxonomic position of an Amazonian endemic. Ann. Missouri Bot. Garden 84: 201
  • Piesschaert F., Huysmans S., Jaimes I., Robbrecht E. & Smets E. (2000) Morphological evidence for an extended tribe - Coccocypseleae (Rubiaceae-Rubioideae). Pl. Biol. 2: 536-546.
  • Puff C., Robbrecht E., Buchner R. & De Block P. (1996) A survey of secondary pollen presentation in the Rubiaceae. Opera Bot. Belg. 7: 369
  • Robbrecht E. (1996) Generic distribution patterns in subsaharan African Rubiaceae (Angiospermae). J. Biogeogr. 23: 311
  • Stoffelen P., Robbrecht E. & Smets E. (1996) A revision of Corynanthe and Pausinystalia (Rubiaceae - Coptosapelteae). Bot. J. Linn. Soc. 120: 287-326.

Desiderata

To further our Rubiaceae research we are interested in:

  • Reprints of all Rubiaceae studies
  • Duplicates of herbarium material from all over the world, but especially from Africa and Madagascar
  • Duplicates of photographs of Rubiaceae
  • Living material (seedlings, seeds) from Rubiaceae worldwide (if possible with a voucher specimen)
  • Leaf material in silica gel, flowers and fruits in alcohol 70% (if possible with a voucher specimen)

In return, we will do our best to provide determinations for all duplicates sent.

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