(Psycho refers to a person’s health and spirit, reflecting medicinal perceptions for some members of the genus. Nervosa refers to the sunken curved leaf veins.)
Rubiaceae, The Coffee Family
Wild Coffee is an abundant native shrub popular in landscaping. So pretty! To dispose quickly of an old question, no, it is not coffee that is wild. The connection of Wild Coffee to Dunkin’ Donuts is merely a superficial resemblance to a true coffee plant and membership among several thousand other species in the vast Coffee Family, along with Ixora, Pentas, Mexican “Clover,” Snowberry, Firebush, and many additional familiar plants. The genus Psychotria itself has over 1500 species, and includes a prime ingredient in hallucinogenic ayahuasca. This has nothing to do with our Florida shrub which gives no high, is not edible, and can reasonably be presumed to be toxic. Wild Coffee is a terrific example of a mechanism to promote cross pollination called heterostyly described several years ago in this blog. CLICK
After a hiatus of some 8 years, here now is a different oddity of Wild Coffee, one repeated among the Rubiaceae. A little context will help:
Stipules are outgrowths in some plants where the leaves join the stem.
The Coffee Family has a peculiar sort of stipules, called interpetiolar stipules, which are flaps connecting the bases of the paired leaves. Each leaf pair has on both sides of the stem a pointed or rounded (or fringed) stipule rising up and pressed against the stem.
At the tip of the stem two stipules cover the growing tip. Think of two hands clasped in prayer with an egg (the growing tip) between them.
Now the interesting part. On the base of the inner face of each stipule is a row of finger-shaped organs called colleters (CALL-eh-ters). You can see older brown or black colleters between leaf bases along the stem where aging stipules have dropped off.
In the stem tip, by contrast, the colleters are fresh, white, and secreting a sticky fluid the color and consistency of Elmer’s Glue which fills the chamber between the stipules.
Botanists have speculated on the function of the fluid. Given that it surrounds the tender growing tip, the standard interpretation is it protects the tip. Okay, but personally I think that’s not the whole truth. As the stipules part and young leaves come forth the young leaf blades are wrinkled and sticky with the white fluid. Seems to me that the crinkling delays direct sun or wind exposure on the emerging leaves, and that the persistent fluid may add protection from drying until the leaves mature a bit.
Time to broaden the perspective. Wild Coffee is a tropical species with a northern extension, growing from hot South America to frosty Duval County (Jacksonville area). Interesting that a tropical species with a toe into the nasty “north” has a well protected growing tip. Plants that evolved in cold climates generally have bud tips encased safely under tiny bud scales to get through the winter. A tropical plant penetrating into harsher climates has to have “its own” protection.
Now don’t get me wrong, I’m not suggesting that the plant developed the fluid-filled stipules in response to its high-latitude expansion. Fact is, many tropical plants have various devices to protect their tips from sun, drying, insects, wind, infections, and more. Perhaps some of those protective mechanisms help certain tropicals expand into climates harsher than where they originated. Like cool counties in Florida. Tropical plants extended into Florida face tough conditions beyond cold. Without a statistical study, I think it safe to say that most of our tropical species live near the warmer yet windier and saltier coasts. And in addition to chilly temperatures we have plenty of blazing heat, dry times, fungi, bugs, wind, and tough livin’.
Let’s look at some additional tropical species with northern limits in Florida and see about their bud protection:
Strangler Fig, Ficus aurea, grows from Central America to Volusia County (Daytona). Its growing tip hides under a thick nose cone formed by the stipule on the topmost leaf.
Red Mangrove, Rhizophora mangle, growing all around the tropical world and extending north to the Florida Panhandle (and rarely farther), likewise has a giant slime-filled nose cone over its bud.
Seagrape, Coccoloba uvifera, is a third species with a bud tip nose cone. It reaches from South America to Flagler County (a little south of St. Augustine). (For those familiar with botanical terminology, the cone is the ocrea.) The cone is filled with a clear gel that might add protection in the bud phase or perhaps by “varnishing” the baby leaf as it grows forth.
Pond Apple, Annona glabra, extending north to Brevard County from South America, has its tender tip hidden beneath the base of the topmost leaf until new growth pushes off the protective older leaf.
We could go on, but that will get boring, especially because the point here is that this is something fun to explore, not to list.