Autumn in North America is automatically associated with vibrant leaf color. Autumn in the Bay Area may not be as dramatic as on the East Coast, but the plants here are also anticipating the changing of the season.
Aside from an unusual sprinkle of rain in July, our landscape has only received fog drip since the last significant rainfall in May. Needless to say, the plants on Alcatraz that do not receive additional irrigation can hardly wait for the first rainfall.
Succulents are well suited to our Mediterranean- like climate; they are just now beginning to show signs of dryness. Many of the signs are actually adaptations to the lack of water. All of the succulents are able to store water in their highly evolved stems, leaves, and/or roots. In fact, when water becomes scarce, some succulents will shed their lower leaves to conserve water. As soon as water becomes available again, the plant begins to store water again in the existing leaves and will grow new leaves as well.
Another response is a change in leaf color. Chlorophyll is responsible for the green that we see in plants; but there are other pigments in plants that give red, blue, orange and yellow colors. It is thought that in response to stress, plants will show pigments that would otherwise be hidden. Anthocyanin and betalain are pigments that give a red hue.
Several succulents on Alcatraz are
now showing their true colors. Crassula ovata, the common Jade plant, normally has a leaf edge ringed in red, but now has the entire leaf deepened in a shade of red and while the red edge is very brilliant.
Aeonium arboreum normally displays a rosette of green leaves; but now each leaf is edged in red, plus the lower leaves have been dropped to conserve moisture. Another succulent, Aeonium cuneatum has also adds to the display of color. This succulent normally is grayish green but has taken on more rosy gray leaves.
Regardless of the cause, the gardener can appreciate the changing seasons and design with the red hues in mind.