Friday Fabulous Flower - pink powderpuffs

Darn such a busy week.  The good news is that a not too violent front delivered nearly 2 inches of rain overnight greatly helping replenish ground water.  Even still our water bill will be a frightful thing.  This week's FFF appears thanks to our neighbors who have this tree in their front yard.  Generally known as mimosa, it's actually Albizia julibrissin. A long-time ago introduction to North America it tends to be a bit invasive and weedy.  Like a lot of fast-growing trees it tends to die back a lot, often dying young, especially here near the northern limits of its cold hardiness (zone 5).  However it is a quite pretty thing and if you know your botany, you recognize the powderpuff flowers and doubly compound leaves as characteristic of a mimosoid legume.  It's fruits are many seeded pods and in warmer climates the germination rate is high.  Powderpuff flowers in general tend to use the stamens as the attractive floral feature.  In mimosas like this the "puff" is actually a whole inflorescence, a ball or hemisphere of flowers, each with flower only has 10 stamens but when clumped together the display is quite showy.  Sticking up among the stamens is a single pistil's style and stigma (whitish filaments sort of sticking out).  Many decades ago when TPP was interviewing for a job in the south, the department chair asked me what I could see as we drove along, "There's nothing there but mimosa trees and a cotton field," was my answer (northern boy passed that test).  

Friday Fabulous Flower - Royal Poinciana

It's the last day of November, and while the local weather is mild, the onset of winter always has TPP longing for the tropics a bit.  So here's a fabulous bit of the tropics, and what may well be the most fantastic of all ornamental flowering trees, the royal poinciana (Delonix regia, Fabaceae).  This is a classic rain tree.  First at maturity the tree has a remarkably broad, spreading, and low crown, clearly not the form of a forest tree, but one from an open, seasonally dry savanna.  While native to Madagascar, where it's endangered in the wild, it's cultivars are found as UTF (ubiquitous tropical flora).  Second, rain trees tend to be big bang flowerers with a large number of flowers open all at once making for a flamboyant display.  Although the scale makes this tree look really low to the ground, you can easily walk under its branches with no danger of bonking your head.  In Queensland a colleague had one of these that covered the whole lawn in front of his house.  Good thing there is no commandment to not covet your neighbors' trees.   

Maniltoa archives

Dear most alert and attentive reader, yes, the Phactor was aware that Maniltoa was featured in a previous blog two years ago, but no flowers were produced with that flush of growth that followed a severe pruning, and the new pictures were so much more handsome, but that post did explain how the branches and leaves repositioned themselves. Thanks for the reminder.

Floral and Foliar Display

This is a spectacular plant called the "cascading bean" (Maniltoa lenticellata - Caesalpinioideae: Fabaceae) from northern Queensland. How one of them got into our greenhouse is a long story, but here 'tis for the past 20 years or so. Actually it's outgrown the greenhouse, twice, and has been severely pruned for its effort. It regularly puts on a growth spurt producing these cascades of new leafy twigs that are pink, almost devoid of chlorophyll, and quite limp, falling out of the large pink buds all at once. Slowly the pink fades to be replaced by pale green and then a darker green, and as that happens the leaves and twigs get pulled up into a graceful arch. This year the leaf flush was accompanied by flowering for even more excitement. Both the pistil and stamens are exerted from a reflexed white corolla. Wow!

Rainforest Field Trip - Corkscrew Flower

This largish, coiled flower (3") reminds many people of a seashell, but this ones smells pretty good. Most of my students guess this is some type of orchid, but the coiled shape fools everyone pretty well and even though most of you would think you knew the family pretty well, you might not figure out that this is a legume, a bean. Now the standard faboid bean flower has 5 petals: an upright standard, a pair of laterals, and two lower petals forming a keel within which the 10 anthers and pistil are located. In many cases a pollinator's weight causes the keel to shift downward so that the stamens or stigma make contact with the pollinator's body. Actually this tropical bean flower (Vigna) works the same way, sort of. The standard petal makes the coil (to the left), and the "laterals" are skewed to the top and bottom (lavendar ones), and the keel within is a long narrow coil. The bottom lateral petal forms the landing pad and weight upon this petal shifts the corolla such that long, coiled style and stigma within the keel push pollen out of the tip of the long, coiled keel, or once the pollen is depleted, just the stigma itself emerges several mm. One of the problems in a diverse ecosystem like a rain forest is having enough pollinators to go around, so to use the same pollinator without getting incompatible pollen clogging your stigma some flowers apply pollen to the top and some to the bottom of a pollinator allowing two different plants to share the same pollinator. Coiled flowers like this legume go one step further in dealing with the dorso-ventral biology of animals. This flower is asymmetrical forcing the pollinator to enter the flower from just one side and the pollen is delivered to and picked up from the left side of the pollinator. If you know how you can make this flower work by just pushing down gently on the landing pad petal. Go ahead, try it!

Identify Friday's Fabulous Flower

This tree in flower isn’t particularly gaudy, but it takes lots of people by surprise, including a couple of my plant taxonomy students. So have a look, and then decide what pretty common and well known plant family does this plant belong in? It’s a bit hard to see, but there are 10 stamens. You get extra credit for getting the name of the plant. Give me your answer before you read on.

This one catches many people by surprise because it really doesn’t look much like a member of the bean family (Fabaceae). In its broadest concept the bean family consists of three big subfamilies, the faboids with the typical bean flower, the mimosoids with flowers in powder puff inflorescences, and the caesalpinioids, which being largely tropical are less familiar to residents of temperate climates. And this species has none of the floral flamboyance of Delonix regia, the royal Poinciana. Most people even fail to notice this tree is in flower, but it has the handsome broad spreading crown of its tropical relative. And several of my students correctly identified this as Gymnocladus dioica, the Kentucky coffee tree (but they were using a plant ID manual).

Jade vine - Another ludicrous flower to enjoy

The jade vine (Strongylodon macrobotrys) is a tropical liana (woody vine) from the Philippines. If you know your plant families, you’ll recognize these flowers as beans/legumes right away (1 standard petal, two lateral petals, and two petals forming a keel housing the stamens and pistil) except what a color! This pale blue-green color is very unusual flower color, but it shows up well in dim light against a dark and green background, which abounds in the rain forest understory where the Phactor works.

Each individual flower is about 2 inches long. And like wisteria, which the Phactor is told flowers, his own vine providing no evidence of this at all, the inflorescence hangs upside down, so each flower twists 180 degrees on its stalk to present itself right side up. Some tropical fruits have a similar pale blue color, again to show up well against a dark background, and the Phactor promises to show you one soon.

The inflorescence of flowers is a foot or two long and hangs down from the vine on long cord-like stems. And this combined with the color tells me that the pollinator is a nectar foraging bat! A similar bean (Mucuna holtonii) grows in the neotropics, but the flower color is just a pale greenish, however the upper petal of this bean’s flower acts as a sound reflector to bounce the bat’s sonic signals back at them (research conducted by Dagmar and Otto von Helversen; you meet the best people while doing field research.). Jade vine is now fairly common in conservatory collections at botanical gardens, like the New York Botanical Garden which is where this picture was taken (eat your heart out GrrlScientist).

The flowers work by lever action. The weight of the bat pushes the keel down forcing either the pollen laden anthers or the stigma out the tip of the keel to make contact with the bat’s body. Unfortunately never having seen bats and the jade vine in action, I don’t know how exactly the two interact, and very unfortunately, the native habitat of both are threatened by deforestation. It’s depressing to know that someday such organisms may only live in cultivation. At least this Asian import won’t escape into the wilds of the Bronx.

Flushed with success

Regular visits to our teaching greenhouse are part of my job and mental health program. Although the facility is not physically impressive, the number and variety of plants contained therein is quite impressive. Interesting observations of exotic plants happen regularly.

Over 20 years ago I brought a small tropical tree seedling back from Queensland Australia. It’s the genus Maniltoa in the legume (bean) family and it now has nearly outgrown the greenhouse. If it were not pushing up against the greenhouse glass this tree’s limbs and leaves would show a graceful arching. But this plant has a most unusual and ornamental feature. It produces huge buds from which emerge whole branches bearing nearly full-sized leaves, but here’s the strange part, these branches and their leaves are pink and totally limp. They dangle down like rags, and since the tree tends to flush, a number of such pink branches emerge from buds all at once. Such flushes of new vegetation are thought to overwhelm herbivores that might attack the new foliage.

Slowly, over a couple of weeks, the pink pigments fade and chlorophyll slowly develops turning the leaves pale green. And then, over another few weeks, the branches and leaves slowly pull themselves up into a rather graceful arch. They accomplish this by having a specialized swollen zone called a pulvinus at the base of leaflets, leaves, and branches. Looking and acting a bit like a knuckle, the pulvinus (see close up on right) reorients the branches and leaves. The same structures close up and droop many legume leaves at night and account for the movement of leaves on the touch sensitive Mimosa pucida, another legume.

So our Maniltoa has provided us with a bit of colorful tropical cheer on a cold, late winter day. Enjoy.