PLANT OF THE WEEK

Dr. T. Ombrello - UCC Biology Department

SENECIOS,

WITH WINDOWS IN THEIR LEAVES

Common names:              Gooseberry; String of Beads  

Scientific names:            Senecio herreianus; Senecio rowleyanus  

Explanation of scientific name:

Senecio – old Latin name – from senex meaning old man, and is said to be an allusion to the hairy fruits produced by the members of the genus Senecio.

The Gooseberry and String of Beads are closely related members of the Sunflower family (Asteraceae).  While they do not look anything like most members of this family (they grow as trailing vines with odd leaves), their small flowers are very similar in structure to sunflowers and asters.  This indicates a close evolutionary relationship, and plant taxonomists have grouped them into the Asteraceae.

Native to the drier regions of southwest Africa, these species are leafy succulents, in that they store large amounts of water in their leaves (as opposed to stems as do the cacti) and can withstand long periods of drought.  Gooseberry leaves are football shaped and about 3/8 inch long. String of Beads leaves are spherical and about ¼ inch in diameter. The unique shapes of the fleshy leaves greatly reduce the surface area exposed to the hot and dry environment, so they lose a bare minimum of the precious water extracted from the soil.  The reduced surface area, however, limits the amount of the sun’s energy the plants can absorb for photosynthesis.  Nature’s way of compensating for this limited external surface area is to have a “window” or slit of transparent tissue in each leaf that allows light to enter and be absorbed by the photosynthetic cells lining the inside.  Therefore, light absorption occurs on the outer surface as well as the inner surface.  This allows the plant to produce a sufficient amount of food by photosynthesis while conserving its water.  The central core of each leaf is composed of clear, non-pigmented water storage cells.

These species are excellent examples of how plants can adapt to become perfectly suited to thrive in even the harshest of environments.