Tuesday, December 26, 2006

Sex and the Gesneriad

Ok, ok... I confess to using cheap advertising tricks to get avid readers. But this morning when I was thinking of what to make a post about I looked back at the last two entries. They're dealing with hybridizing and the resultant changes that can be induced in a plant because of the different methods of dealing with seed production. My Google searches today seemed to only want to talk about vegetative propagation (propagation by using leaves or pieces of plants) and not sexual reproduction (the seed production.) When I wanted to find out what the typical characteristics of a "gesneriad" are and what makes that unique from other families of plants (especially regarding their seed production and formation) I found a surprising lack of information.

I did a little digging and found that in a very nice book published thirty years ago called "Miracle Houseplants" by Virginie and George Elbert, I could find out what characterizes a gesneriad flower and what relates these plants that may not necessarily strike us as related. Why, for instance, is the African violet that we all grow said to be related to a strep or a sinningia? Well, it all has to do with the way the flower is constructed!

With help from the Miracle House Plant book, here's a summation of the features that distinguish a gesneriad from all other types of plants. The flowers have petals that are joined at the base so that they're reduced to being the lobes of a tube - think streptocarpus flowers. This tube (although sometimes short like in the African violet) usually has five lobes. The flower has two smaller superior (top) lobes and three larger inferior (bottom) lobes. The calyx is five parted and lies between the flowering stalk and the corolla (or petals) of the flower.

The ovary is superior and one celled and it contains a large number of ovules which develop into lots of small seeds. There are two to four stamens (the pollen or male part) which are usually fused in pairs or joined. The flowers can be typically borne in pairs on a peduncle (flower stalk with multiple buds) or on a pedicel (a flower stalk with a single bud) from the axils or nodes of the leaves.

The gesneriad leaf is simple. It isn't made of multiple leaflets nor is it deeply notched. Usually the leaf is oval or spatulate. There are lots of different forms of gesneriads though, including terrestrial and epiphytic (hanging in trees) herbs, as well as more woody shrubs and small trees.

The small seeds are many and usually in a seed pod that is not compartmentalized. The plants have a variety of root forms including the fibrous, (like African violets) tuberous, (like Sinningia) and rhizomatous (like Eucodonia). Certain gesneriads bear propagules in the axils of the leaves which are similar to undergrownd rhizomes. A few posts back there was a picture of a propagule.

And finally, in some of the gesneriads only one half of the cotyledon (both halves of a dicotyledonous seed) continue to grow after germination. This gives us the unifoliate streptocarpus and the like.

When the taxonomists are identifying a new plant they look at a number of characteristics. Sometimes a plant will display traits that might fit into more than one category. That's why a plant will sometimes be reclassified and have it's scientific name changed after being in a particular group for years. The characteristics that we have just discussed determine what we enter in our shows. It is the reason why we can't enter our great looking lily or rose in the "blossoms with white flower" class. Now we can go forth into the rain forest and impress our tour group with how many gesneriads we can identify from just their flowers??? Well....

No comments: