Wednesday wildflower: periwinkle

Plants that are poisonous are a nuisance and a hazard, but they can also be very useful. The family Apocynaceae is rich in poisonous plants (e.g., oleander) and some of their toxins have medicinal properties.  In particular the widespread tropical weed Catharanthus roseus, rosy periwinkle, produces several drugs that inhibit cell division, thereby slowing the proliferation of cancer cells.  The drugs do this by inhibiting the growth of the spindle in cell mitosis.

The common periwinkle, Vinca major (also known as myrtle in the USA) also produces toxic alkaloids, but these don't play any major role in evidence-based medicine.  Mabberley (2008) mentions vincamine is used for cerebral vascular disorders, although it's now synthesised from a different plant extract.  Locally in its native range, Vinca is used in herbal medicine for treating cuts, toothache, and as a sedative.  Five species are known, ranging from Europe to N. Africa to C. Asia (Mabberley 2008).

Periwinkle, Vinca major.  Karori.

It is however a common weed or wildflower in New Zealand.  We have two species, V. major and V. minor.  V. minor has sessile leaves, or at least very short petioles, and smaller flowers.

Periwinkle, Vinca major, Karori.  A shoot with a bud and opposite leaves; an opening bud, enlarged; leaves, upper and lower surfaces; and a flower.  All line scales 10 mm.

The overlapping of the corolla lobes in the bud (above) is found in many species of the family, such as frangipani, but it's by no means unique to Apocynaceae.  Periwinkle is widespread in New Zealand, including Stewart Island and the Chatham Islands (Webb et al. 1988)

References

Mabberley, D.J. 2008.  Mabberley's Plant Book. Cambridge.

Webb, C.J.; Sykes, W.R.; Garnock-Jones, P.J. 1988.  Flora of New Zealand Vol. 4.  Botany Division, DSIR.