Botany Photo of the Day

Thank you to Quentin Cronk for both today's photograph and accompanying written entry. – Daniel.

Barnadesia spinosa L.f. (Asteraceae) is shown here, growing at the site of the old Inca ruins of Inga Pirca, Ecuador (c. 3000m elevation). It is a spiny shrub to about two metres, often found growing at the margins of fields at high elevation. The spines are effective in protecting it from grazing by llamas.

Barnadesia is one of the most interesting members of the daisy family or Asteraceae. In 1987, Jansen and Palmer discovered that the whole family Asteraceae (some 20,000 species) shared a 22 kilobase inversion in the chloroplast DNA, with the sole exception of the Barnadesia group (88 species), which had normal chloroplast DNA. These results are strongly suggestive that a split between the Barnadesia group and the rest of the Asteraceae was the earliest evolutionary event in the family, and this has been confirmed by subsequent research.

The Barnadesia group was therefore described as a separate subfamily, Barnesioideae K. Bremer & R.K. Jansen. This subfamily is defined by the axillary spines of a type unique in the family, and by a unique type of long unicellular hair that is found on all parts of the capitulum. Subfamily Barnadesioideae comprises the genus Barnadesia and eight related genera also from South America (including Arnoldoa, Chuquiraga and Dasyphyllum).

Barnadesia has some 20 species distributed down the Andes from Colombia to Northern Argentina; for further information see the account of Barnadesia in Arboles y arbustos de los Andes del Ecuador (in Spanish).