Flowers and fruit - a short lesson

A flower/fruit garden question, one of TPP's favorite things.  The question was simple this person's cucumber plants had plenty of flowers, but was producing no fruit, no cucumbers.  This is definitely a problem that will probably get fixed shortly.  The reason this happens is that cucumbers have two kinds of flowers, the botanically naïve call the "male" and "female" but this is quite incorrect, although this understanding of things quite often prevails.  Superficially both flowers look a lot alike so that bees get fooled into visiting the rewardless female flowers.  Funny how many people don't notice this.  The botanical term for this is monoecious, technically one house (but two bedrooms is you want another understanding.)  So look closely at the flowers on your cucumbers.  The "female" flowers have little cucumbers just below the yellow perianth.  "Male" flowers don't.  Virtually all cucumbers start out male as these flowers are cheaper to make, but as the plant gets bigger, some female flowers appear, and if pollinated, begin developing into cucumbers, fruits that we eat at a juvenile stage.  The image borrowed from somewhere shows a male flower to the left and the female flower to the right.  The anthers and the stigma look a lot alike, so bees looking for pollen make mistakes, foraging errors that effect pollination.  Or you can do it yourself with a small brush.  Some varieties of cucumber only produce female flowers, so you must plant a pollinator plant  The seed packet will have some seeds dyed green so you can see the males, and if you don't do this (TPP made this mistake once.) you'll get lots of females but no fruit, unless you borrow some male flowers from a neighbors' garden.  If you don't understand why male & and female are wrong, here's link to a blog that explains what pollen really is.  

Nocturnal pollination

Most people don't realize that many plants flower and interact with pollinators at night, particularly in the tropics.  An article in the latest American Journal of Botany provided a nice image of a hawkmoth, an insect version of a hummingbird, visiting a night-blooming plant (Oenothera harringtonii). Notice that the flowers are white and don't actually open very much except at the top of the corolla, but the stigma is exposed. The long proboscis of the hawkmoth is inserted to get a reward delivering and withdrawing pollen in the process. This is a terrific image for teaching, and a very interesting study (open access): Land-use change has no detectable effect on reproduction of a disturbance-adapted, hawkmoth-pollinated plant species, a study by my very talented Chi-town colleague Krissa Skogen and her collaborators (November 2016 vol. 103 no. 11 1950-1963). 
Enjoy!

The apple crop

TPP has not had the best luck with apples.  Previous attempts to have a few apples have been failures in one way or another. The most recent failure was a dwarf Novaspy, the first time Northern Spy has been successfully dwarfed. Of the two trees planted, both were initially vigouous and one flowered and fruited nicely in its 3d year, but then it went into a decline and died. The 2nd tree stayed vigorous, but it never flowered and fruited and seemed determined to grow into a larger sized tree. The one crop of apples was great, real Northern Spys, a superb variety that is hard to find.  
So try, try again, and two Colonnade apple trees were planted, both the same variety, Flamenco, derived from orange pippin ancestry. These are a columnar dwarf, growing 10-12 feet tall and 3-4 feet in diameter, and the nursery stock was beautiful. However a pollinator was needed and only one variety of Colonnade was available, so an Urban Apple columnar tree was gotten from another vendor. This was a Tart Lime, a granny smith type apple that TPP was not so keen to have, but biology. This tree was half as big and half the price (notice how that works),  but the flowering of these varieties may not work out in terms of flowering time, but no matter as the Colonnade trees did not flower in their 2nd season, while the Urban Apple did. Now crab apples of the ornamental type can pollinate apples if their flower color is similar. And the image above shows the apple crop, the whole apple crop, one apple, on the tree bought as a pollinator.  It's a start.

Friday fabulous flower - yucca in contrast

This is just your basic yucca although with variegated leaves, but it is a bit more dramatic because here it is standing in front of a weeping copper European beech and the dark purple of the leaves makes the creamy yucca flowers stand out.  Yucca demonstrates and interesting pollination biology called an obligate mutualism. The yucca gets pollinated only by yucca moths and then in a very specific manner. The yucca moth female lays her eggs inside the pistil of the flower, and then she gathers a ball of pollen, climbs the style and places the pollen directly upon the stigma to assure that her offspring have ovules, developing seeds, to consume. The egg laying is gauged such that not all of the seeds get consumed. This is the only place the moth can reproduce, so each party, the plant and the moth, absolutely require each other to reproduce; both parties benefit and both parties need each other. However since humans cultivate the yucca it can be grown in places where the moth does not live, and people can also pollinate the flowers to make seed. Yucca isn't native to the upper Midwest, but in places the moth does exist interacting with this rather common introduced ornamental

Pollination success - waiting, waiting.

TPP's apple and pear trees have flowered, and it wasn't the absolute best weather for flowering, and we had a close call the other night with a low temperature near freezing, so now just waiting to see if we have pollination success.  Last year an early spring and a late freeze combined to nuke the entire upper midwest apple crop.  It was grim.  Had to have northern spys shipped in from NY.  It's just a tad to early to judge whether the pollinators did their job or not. Plenty of crab apples were in flower too, so lot's of nearby pollen sources, and no crab apple pollen will not affect the apples, just the apple offspring (seeds).  The pear tree did not flower well, so the display might not have been big enough for good pollination.  Combination of drought and bunnies required redoing most of the raspberry bed this week as well, and this was after giving up on the blue berries.  In the process discovered that the neighbors property adjoining ours is raising a bumper crop of garlic mustard. Each year their seeds repopulate our gardens, so no matter how zealously the Phactors weed, we get more.  Does the military sell surplus flame throwers?  TPP will attempt to widen the weed-free zone along the fence line (on their side!) one way or another.  But guess we're to gardening as Cub fans are to the Cubs, always hopefull, often disappointed.      

Figgy fruit

With a few minutes to spare, which is largely an illusion, so let's say, while wasting a few minutes, TPP stepped into our teaching greenhouse a few short steps from his botany classroom to inhale humid air laden with the smell of luxuriant plant growth.  Especially in the winter this is great therapy.  And there on the floor was a strange, slightly bell-shaped, and for an indoor plant, unusual fruit upon the floor beneath a potted banana (no, clearly not a banana), which was under a Gnetum (which is a gymnosperm, so quite impossible as a fruit producer although it does have a somewhat fleshy seed coat), and so further up was the source.  The entire north end of our glasshouse is home to a quite large fig, the creeping fig, Ficus pumila.  Although rather hard to find and seldom noticed the trunk of this vertically sprawling/climbing fig is about 15 cm in diameter.  And most certainly the fruit was an immature fig syncomium.  This is a tough fruit to understand, and a tough one to explain (TPP has tried before).  OK, lets start with a strawberry.  The fleshy "fruit" is the receptacle (an accessory fruit) and the many pistils of the strawberry flower form fruitlets, little achenes on its surface.  Now if instead of achenes they were drupelets like in raspberries, and if instead of being individual pistils in a single flower they were each a flower, and instead of being bisexual as in the strawberry, the flowers were unisexual, and if the entire thing were then turned inside out, well, simple as that, you'd have a syncomium.  The fleshy outer wall is the receptacle, and on the inner facing wall are unisexual flowers, whitish, male pollen-producing flowers just below the apex (although the syncomium is often pendant) and below them reddish female fruit-producing flowers (Thanks to Gerry Carr for posting this image).  Each fig is pollinated by a species of wasp that requires the fig as a location for mating and rearing its young, and enclosed the way they are, figs also need this particular pollinator, producing an obligate mutualism.  Here's a link to this interaction diagrammed.  Female wasps carrying pollen enter through the apical pore (left) where the inward orientation of bracts prevents leaving.  The next generation of female wasps require males, who never leave the syncomium (try not to think about this too much when eating your next newton) to chew an exit through the syncomium wall.  See, time well wasted.

Who gives a fig?

Rachael Roscata asks: "So not to go on a tangent and cause a billion questions beginning with "Well what about...", but what about a fig? Is it a fruit?"
Well, the Phactor doesn't have to go out on a limb (?) to answer this. A fig is a real fruit, but a very strange one. Rachel found the Phactor's 3-yr-old blog about whether an artichoke was a fruit or a vegetable, a blog read by over 5,500 people since the software began keeping track of traffic.
A fig is a multiple fruit, and an accessory fruit, one composed of a whole inflorescence of flowers that develop enmass into a single fruit. A fig is a synconia, a bulb-shaped receptacle, a modified stem bearing many flowers on its inner surface, so you never see fig flower unless you cut the whole synconia open. So how do it get pollinated? Tiny wasps live and reproduce inside the synconia. Male figs don't produce fruit but they provide a brood substrate for wasp larvae and pollen, which is carried upon female wasps seeking new synconia in which to lay eggs. The pollinated female flowers produce the edible fruits, each flower resulting in a single seed. Each species of fig has a specific and different species of wasp, an interesting evolutionary dance where each species needs the other for its reproduction. Fig flowers are very small, so the actual flower-fruit would be just one of the sort of stringy units within a fig, but the receptacle also develops into fleshy tissue. As pointed out in the artichoke blog, accessory fruits include fleshy tissues associated with the flower or flowers. But Rachael was pretty perceptive in thinking that a fig was a pretty strange fruit. Well, what about that! Try not to think about what happens to the wasps after pollination, but you know those little crunchy bits? They're seeds.

Choosy plants & picky flowers

When choosing a mate, lots of animals are choosy; females look for desirable traits exhibited by males, and males often compete for females. Although it surprises many people, plants do the same thing, it's just harder to document. In seed plants, pollen grains are tiny males that disperse to find females, and they may have to compete to acquire a mate. In flowering plants pollen landing on a stigma must race to get to the females by growing pollen tubes to the ovules across a distance equivalent to a marathon in comparison to their size. In this way certain genotypes have an advantage, and it's been shown that these will make larger, more vigorous offspring. And it's not just the males because the floral tissue and the females within may exert influences that make certain genotypes successful or unsuccessful at mating. This and many other studies have found diverse ways in which plants select among available genotypes, choices that involve no thought obviously, but choices nonetheless, for producing their offspring (embryo within seeds). Here's a nice article about several recent studies to give you a new or greater appreciation of what goes on with flowers and pollination.

Orchid pollination and fungus mimicry

Orchids are a fantastically diverse family of flowering plants that employ many fascinating and equally diverse pollination biologies. Animals used as pollen vectors don't pollinate flowers because they like them or anything like that; they visit flowers because they get a reward or they have been fooled, tricked. Some orchid flowers mimic female insects and get males to visit the flower and transfer pollen while attempting to mate with the flower (pseudocopulation). My old friend Peter Bernhardt (He shares an undergrad alma mater with the Phactor.) is among a group of botanists who very recently described a very unique mimicry involving a ladyslipper orchid (Cypripedium) native to China. The leaf spots look like a fungal infection and the flower produces fungusy odors thus attracting a fungus-feeding fly to transfer pollen, a whole new mimicry for a whole new group of pollinators . This is a great looking little orchid (scale bar = 2 cm). Is that cool or what!

Of insects and flowers and things

One of the great biologists of my generation was Thomas Eisner, and we were saddened by his recent death. He studied many things and used his cleverness to figure out a great many ways with which insects interacted with the rest of the world. A very nice post on some of the highlights of his career can be found at the Artful Amoeba, a very fitting tribute to his career. The Phactor heard Tom give several lectures and they were always interesting, and a couple of my colleagues studied with Eisner too. Just excellent biology.

Friday Fabulous Flower - Clusia

Nothing like a tropical flower to brighten a February Friday. This is Clusia uvitana (Clusiaceae or Guttiferae) and the whole plant is pretty interesting. This species can grow like a strangler fig where its seedlings sprout up in a tree, its roots growing down and its crown growing up until it replaces its former host. Like figs it exudes a latex when injured. Most of the species are dioecious (two-housed), which means pollen flowers and fruiting flowers on separate trees. The flowers are fairly large, in this case about 5 cm across when open, and the perianth is very waxy, looking quite artificial to some respect. Pollen and fruiting (this one) flowers look similar. But the most interesting thing is that a resin exudate is used as the floral reward for small bees(lower left, look closely) who collect it for nest building.

Islands in the sky

Islands have many biological oddities because the organisms there are isolated from those on the mainland and this can have many consequences. Unless you are a biologist you probably don't think about mountains tops and the species living there as islands yet they are. One question of interest is determining how much gene flow exists between populations on different islands, and one of my colleagues, Andrea Kramer, has been examining this by looking at bumblebee (see image) and hummingbird pollinated penstemons, and she found that the bee-pollinated species were more distinct mountain to mountain. This means as you may suspect that birds are better at moving genes greater distances than bees. Genetic diversity on mountain top islands is a particularly critical thing to study because a warming climate pushes alpine species higher, and if the mountain isn't tall enough, that population become extinct, and the islands getter smaller, fewer, and farther apart. Islands in the sky may be one of the places where climate change results in the loss of a lot biological diversity especially those that are highest, the inhabitants of alpine tundra. As a change of pace, alpine tundra will be featured in a few upcoming blogs.

Friday Fabulous Flower - Banksia

To get a Friday Fabulous Flower the Phytophactor had to reach far afield, half way around the world into the southern hemisphere. Although widely refered to as Banksia "flowers" , a name honoring the botanist Joseph Banks, this is actually a whole inflorescence of tiny flowers borne closely together in pairs. Pollination is accomplished by the pollinator crawling over the surface of this "bottle brush" going flower to flower or sort of poking into the "brush". Since they are a rich source of nectar the pollinator could be a bird, a small possumy mammal, or a bat, or some combination thereof, and because the latter two are largely nocturnal the flowers are often fragrant at night. Above the flowers and oriented sideways is one of last season's infructescences. The individual fruits are quite hard and often do not open until they have been heated, an adaptation to fire ecology. And of course these are the stuff of Australian children's tales, the evil banksia men who are always on the outlook for unsuspecting gumnut babies.