Blooms in orange
by Ruth Jolly
Title
Blooms in orange
Artist
Ruth Jolly
Medium
Photograph - Photography
Description
Cactus flower anatomy has received little attention. Flowers are large and showy in many genera, with dozens of petals and stamens rather than just the 5 or 10 of each as we might expect of a dicot. All cacti, other than a few species in Pereskia, have an inferior ovary, and that is the point of this portion of the website. The ovaries of cacti are not merely inferior, they are spectacularly inferior. Although axillary buds produce flowers, they always produce a bit of stem tissue first: the very first appendage primordia are leaf primordia, not sepal primordia. In most cacti, the axillary bud apical meristem actually produces 20 or 30 or more leaf primordia before it actually switches over to producing floral appendage primordia. The noteworthy thing is that these leaf primordia typically develop much more than do other leaf primordia on the same plant, and they mature into large scales that may be a centimeter or longer and have a thin, flat lamina-like region. People typically do not realize that these cactus leaves are true leaves but they are true. They are usually called scales or bracts but that does not matter: they are leaves. The problem is that the ovary is so deeply inferior that these leaves appear to be part of a flower rather than part of a vegetative stem
Another aspect of extremely inferior ovaries in cacti: in Calymmanthium, the vegetative tissues extend to the very rim of the tube as expected of cacti, but the rim itself does not expand much during flower development. The rim remains a microscopically narrow hole that is the same diameter as when the floral apical meristem formed it whereas in all other cacti the rim grows along with the rest of the flower, forming a wide rim that bears many petals (look at the flowers on the top of this page). Because the rim does not widen during development, a Calymmanthium flower develops inside a pouch of vegetative tissue -- when the flower is ready to open, it actually has to tear the vegetative tissues apart before the petals can emerge. Fine Art America watermark will not appear on purchased artwork.
Uploaded
December 16th, 2012
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