Coussareeae

Faramea cf. multiflora, copyright Scott Zona.

Belongs within: Rubioideae.

The Coussareeae are a small but morphologically diverse group of flowering plants found in the Americas, many of which have tetramerous flowers, flattened berry-like or thin-walled capsular fruits, and flattened seeds (Bremer & Manen 2000).

Neotropical rubioids

I’m sure I’ve said this many times before but the advent of molecular analyses allowed the recognition of numerous clades of plants that went previously unidentified. Among these novel clades are the Coussareeae as defined by Bremer & Manen (2000), a tribe of Neotropical members of the family Rubiaceae.

Cruckshanksia hymenodon, copyright Scott Zona.

Prior to the tribe’s re-organisation, the current representatives of the Coussareeae were divided between three tribes: the Coussareeae, Coccocypseleae and Cruckshanksieae. This dissolution reflects their diversity of form, from herbs to trees, with tetramerous or pentamerous corollas, producing fruits varying from papery capsules to fleshy drupes. Though consistently well supported by molecular analyses, morphological support for the broader clade remains elusive. Ten genera are currently included in the Coussareeae, with about 330 species all up, all found in Central and South America. A single African genus, Schizocolea, has historically been associated with the tribe but recent authors have supported its assignment elsewhere (Delprete & Jardim 2012).

Coccocypselum lanceolatum, copyright Mauricio Mercadante.

A detailed analysis of relationships within the Coussareeae by Löfstrand et al. (2019) identified three major clades for which supporting morphological features could be identified. As noted by the authors therein, these three clades more or less correspond to the originally recognized tribes; one might argue whether ‘tis preferable to represent the broader relationships revealed by the molecular data or utilize smaller but more easily recognizable taxa. The first subclade includes the genera Heterophyllaea, Oreopolus and Cruckshanksia, united by the production of papery, loculicidal capsules as fruits and found growing in upland habitats in the Andes of Bolivia, Argentina and Chile. Members of this group mostly vary in habit from subshrubs to small trees with one species, Cruckshanksia pumila, being a desert ephemeral. Flowers have salverform, pentamerous corollas. Oreopolus and Cruckshanksia have yellow corollas whereas all other Coussareeae produce white or blue flowers.

Coussarea albescens, copyright Alex Popovkin.

The Cruckshanksia group forms the sister clade to the remaining Coussareeae, most of which produce tetramerous flowers (with the exception of the genus Hindsia). The overall shape of the corolla varies from salverform to funnelform. Members of these clades are more widespread across the Neotropics than the Andean Cruckshanksia group. Thick-walled, septicidal capsules are characteristic of a clade including the genera Standleya, Bradea, Coccocypselum, Hindsia and Declieuxia, whose representatives vary from herbs to small trees. Their sister group is formed by the shrubs and trees of the genera Coussarea and Faramea which produce fleshy, indehiscent fruits. Apparently, there’s a bit of disagreement about whether the fruit of the Coussarea group count as drupes or not (a ‘drupe’ being a fleshy fruit with a single seed that is surrounded by a hardened coat derived from the ovary wall, such as a plum or peach). Though mature Coussarea-group fruit usually contain a single seed, the flower contains two ovules. One of these ovules is usually (though not always) aborted during the course of fruit development.

Cegadera Heterophyllaea pustulata, from Instituto de Botánica Darwinion.

Most species of Coussareeae have little direct economic significance, though they may be environmentally significant through such roles as food sources for birds. A notable exception is the cegadera Heterophyllaea pustulata, a two- to three-metre tall bush found in northwest Argentina. This plant is toxic to livestock, causing photosensitive conditions when eaten such as dermatitis, conjunctivitis and even blindness (Núñez Montoya et al. 2008). Fatalities caused by cegadera have not been confirmed, but losses due to poor condition may still be significant. And besides, it’s just not nice for the sheep.

Systematics of Coussareeae

Characters (from Bremer & Manen 2000): Herbs (creeping in Coccocypselum), subshrubs, shrubs, or small trees. Stipules entire, cleft, as a ridge with appendages, or deeply bilobed. Flowers homo- or heterostylous, often tetramerous, white, blue, or bright yellow (Cruckshanksia, Oreopolus). Ovary 1–2-1ocular, with 1–2 or many (Coccocypselum) ovules per locule. Fruits often flattened (not Coccocypselum), fleshy, white (Coussarea) or often blue (Faramea, Coccocypselum) berries, schizocarps (Declieuxia), or thin-walled capsules (Cruckshanksia, Oreopolus), with 1–2 or many seeds, often flattened. Pollen 3-colporate or 2–4-porate. Chromosome basic number x = 10, 11? with 2- or 4-ploidy level.

<==Coussareeae [Coccocypseleae, Cruckshanksieae]
    |  i. s.: Cruckshanksia hymenodonBM00
    |         Oreopolus glacialisBM00
    |         Declieuxia fruticosaBM00
    |         HeterophyllaeaBM00
    |         SchizocoleaBM00
    |--Coccocypselum hirsutumBM00
    `--+--CoussareaBM00
       |    |--C. contractaBM00
       |    `--C. macrophyllaBM00
       `--FarameaBM00
            |--F. multifloraBM00
            `--F. porophyllaBM00

*Type species of generic name indicated

References

[BM00] Bremer, B., & J.-F. Manen. 2000. Phylogeny and classification of the subfamily Rubioideae (Rubiaceae). Plant Systematics and Evolution 225: 43–72.

Delprete, P. G., & J. G. Jardim. 2012. Systematics, taxonomy and floristics of Brazilian Rubiaceae: an overview about the current status and future changes. Rodriguésia 63 (1): 101–128.

Löfstrand, S. D., S. G. Razafimandimbison & C. Rydin. 2019. Phylogeny of Coussareeae (Rubioideae, Rubiaceae). Plant Systematics and Evolution 305: 293–304.

Núñez Montoya, S. C., L. R. Comini, B. R. Vittar, I. M. Fernández, V. A. Rivarola & J. L. Cabrera. 2008. Phototoxic effects of Heterophyllaea pustulata (Rubiaceae). Toxicon 51: 1409–1415.

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