Solanum rostratum

Taxonomy 

Name: Solanum rostratum Dunal (Solanaceae).

Common name: Buffalo bur.

An annual, self-compatible herb, originally from North America (Whalen 1979), but first introduced in the United Kingdom in the late 1800's. Individual plants reach 1-1.5 m tall, have once or twice pinnatifid leaves, and abundant prickles on the stems and leaves. It produces yellow flowers with pentagonal corollas 2-3.5 cm in diameter and weakly bilaterally symmetric (Whalen 1979). In its native range S. rostratum is pollinated by medium- to large-sized bees including bumblebees (Bowers 1975). Flowers bear two sets of anthers that are unequal in size and may be distinctly coloured (Vallejo-Marín et al. 2009). The fruit, a berry, is enclosed by a prickly calyx and the seeds are released when the berries dry and split while still attached to the plant.

Chromosome No.: n = 12 (Whalen 1979); 2n = 24 (Stace 2010).

Solanum rostratum

Photography: M. Vallejo-Marin

Distribution 

It has historically been reported in England, Wales and Scotland with most records found in the South. However, being an introduced species with an annual life-history, previous records do not necessarily represent stable populations. In other areas where it has been introduced, it usually occurs as a weed of pastures and agricultural fields. In its native range in Mexico it is often found on roadsides and fallow fields as well.

Solanum rostratumSolanum rostratum

Photography: M. Vallejo-Marin

BSBI Hectad Map 

Click on the map to view full-size on the BSBI Maps Scheme website.

Ecology 

A persistent weed of disturbed sites and agricultural fields in its native range. It is poisonous to livestock and humans and may contaminate cereal grain (Parsons and Cuthbertson 2001). Populations in the native range can be composed of several hundreds of individuals, and once a population becomes established it is difficult to eradicate it. Individuals become reproductively mature as early as 4-6 weeks after germination, and a large plant can produce several hundreds of seeds. There are currently no detailed studies of the dispersal of seeds, but dispersal might be achieved by a combination of gravity, water transport, and perhaps secondary bird dispersal. No studies are available on the ecology of this plant in the UK, and its potential for becoming a noxious weed here has not been established.

Status 
  • Origin: neophyte.
  • Rarity: it appears to be quite rare in Britain and entirely absent from Ireland.
  • Threat: it is unknown whether the long history of this species in the UK represents the footprint of multiple independent introductions into the country, or of short-lived but persistent scattered populations.
  • Conservation: as a non-invasive alien, it appears to be of little consequence to nature conservation.
Further Work 

Virtually nothing is known about how this alien species reproduces in the novel pollination environment imposed by British bees, and whether biotic or abiotic factors are more important in limiting its spread here. In its native range, this annual weed depends on visitation by relatively specialized pollen-foraging bees to set seed, and the relationship between floral morphology, pollinator visitation, and reproductive success of this species has been studied in detail. Currently, studies are being carried out to investigate how this non-native cross-fertilizing weed may reproduce in the absence of its native pollinators.

Have you seen this species?

We are calling for the help of BSBI and its members to locate populations of S. rostratum in the UK. If you have seen a plant of this species, please get in touch with Dr. Mario Vallejo-Marín (contact details below). Please send details of location, presence of fruits or flowers and approximate number of plants.

  • School of Biological and Environmental Sciences
  • University of Stirling
  • Stirling, FK9 4LA.
  • Scotland.
  •  
  • Email: mv9@stir.ac.uk
References 
  • Bowers, K.A.W. 1975. The pollination ecology of Solanum rostratum (Solanaceae). American Journal of Botany 62: 633-638.
  • Parsons, W.T. & Cuthbertson, E.G. 2001. Noxious weeds of Australia. Inkata Press Melbourne & Sydney.
  • Vallejo-Marin, M., Manson, J.S., Thomson, J.D. and Barrett, S.C.H. 2009. Division of labour within flowers: Heteranthery, a floral strategy to reconcile contrasting pollen fates. Journal of Evolutionary Biology. 22: 828-839.
  • Whalen, M.D. 1979. Taxonomy of Solanum section Androceras. Gentes Herbarum 11: 359-426.
Citation 
Vallejo-Marin, M. (Date accessed). Species account: Solanum rostratum. Botanical Society of the British Isles, www.bsbi.org.uk.

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