The Biosphere Blog

The Spermatophytes

The spermatophytes are the seed-producing plants, of which there are two groups: the Gymnospermae which produce cones, and the Angiospermae which produce flowers and fruit.

Gymnospermae

Gymnospermae, also called gymnosperms, are the oldest of the two groups, and date from about 319 million years ago in the late Carboniferous period.
‘Gymnosperm’ is from the Ancient Greek γυμνός, gymnós, ‘naked’, and σπέρμα, seed: ‘naked seed [seed not enclosed (by a fruit)]’.

Gymnosperms produce cones, and include conifers, cycads, gnetophytes, and the sole surviving ‘living fossil’ of its group, Ginkgo biloba (the maidenhair tree).

Angiospermae

Angiospermae, also called angiosperms, are the flowering plants, and the earliest known fossil (of pollen) dates to around 134 million years ago in the Cretaceous period. The earliest known plant fossil dates from 125 million years ago, also in the Cretaceous.
Angiosperm’ is from the Ancient Greek ἀγγεῖον, angeîon, ‘vessel, jar, receptacle’, and σπέρμα, seed: ‘seed in a container (fruit)’.

Angiosperms produce flowers, and from those, fruit.

The jujube tree, Ziziphus jujuba Mill. is both a spermatophyte and an angiosperm.

Spermatophyte Reproduction

In Gymnospermae

Cones are the sex organs of gymnosperms. Male cones produce pollen (made of pollen grains which contain sperm), and their female counterparts produce ovules (which contain unfertilised egg cells). Cones are thus unisexual, either male or female.

In Angiospermae

Flowers are the sex organs of angiosperms. Like cones, flowers also produce pollen (also comprised of sperm-containing pollen grains) and ovules (also comprised of egg cells). But unlike cones, which are only ever male or female, flowers can be one of four basic types as shown in the illustration below:

Flowers

Dioecious Species

Dioecious species are those with distinct male-only and female-only plants. While about 65% of gymnosperms are dioecious, only about 6% of angiosperms are. Male-only angiosperms produce male-only flowers and female-only angiosperms produce female-only flowers. Dioecious angiosperms thus produce unisexual flowers.

[An example of a dioecious angiosperm is the weeping willow (Salix babylonica).]

Monoecious Species

Monoecious species are those with either distinct male and female sex organs on the same plant, or, specifically in the case of angiosperms, flowers on the same plant with both male and female parts.

Although about 65% of all gymnosperms are dioecious, almost all conifers (which are gymnosperms) are monoecious and produce both male cones and female cones on the same plant. But we shall leave gymnosperms here, and focus solely on angiosperms from hereon in.

As with dioecious angiosperms, the flowers on monoecious angiosperms which are either male or female are also unisexual flowers. The flowers on monoecious species which contain both male and female parts are called bisexual, hermaphroditic, or perfect flowers.

The jujube tree Ziziphus jujuba Mill. is a monoecious species, and its flower is a perfect flower.

Dichogamy

Some animals change sex during their life — the clownfish is just one of many examples — and this is called sequential hermaphroditism in animals.

A change from male to female is called protandry (or protoandry), and from female to male is protogyny.

Sequential hermaphroditism in plants is called dichogamy. The striped maple (Acer pensylvanicum) appears to change sex to female or female and male in response to damage or disease, and every species within the Arisaema plant genus changes its sex either from year to year or as it gets bigger over the years.

Sequential hermaphroditism, whereby the plants change sex, is actually very rare in botany. More common is the sequential hermaphroditism (dichogamy) of flowers. However, the term in this context doesn’t mean that the flowers literally change from male to female or vice versa, but that the male and female parts develop at different times.

Dichogamy exists in both monecious and dioecious angiosperms.

Dichogamous flowers can be either protandrous, where the male unisexual flowers, or male parts of bisexual flowers develop first, or protogynous, where the female unisexual flowers, or female parts of bisexual flowers develop first.

In the Jujube Flower

For now, please note that the jujube flower is protandrous. Its male parts develop ahead of the female parts. We shall explore the details of this, and its significance, in future chapters.

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Around 7pm the other evening I was perusing my trees, and — as I often do, gently pulled down a fruiting branchlet above to look more closely with my loupe at the flowers and developing fruits along it. To my absolute horror it came away in my hand! I reconciled myself by thinking that maybe it was structurally weak and always destined to fall off, and decided to make good of the situation by writing about it!

So here it is, the anatomy of a Shanxi-Li fruiting branchlet!

This was a large branchlet, about 385 mm along a straight line, but closer to 405 mm long, as measured by following every bend of the stem with a piece of string and then measuring the string. It was so noticeably large (most in my experience tend to be under 300 mm long) that I really do wonder if it was structurally weak and would have snapped off eventually as the developing fruit on it grew larger and heavier?

As with all new jujube branch growth during a season, the oldest part of this branchlet (which was closest to the fruiting mother branch) was turning red while the youngest part of the shoot was still the bright green of new growth.

The proximal end (of anything) is that closest to the point of origin or attachment. Here, the point of attachment of this fruiting branchlet was the fruiting mother branch. Conversely, the distal end (of anything) is that furthest away from the point of origin or attachment:

Here is where the point of attachment was:

And here is the proximal end of the branchlet, with a transverse (crosswise, cross-sectional) view of the point of detachment:

A node is the point along a branch from which leaves and other branches grow. An internode is the interval between two nodes.

The closest node (and leaf) to the fruiting mother branch was 15 mm away. The largest internode, and the third along from the fruiting mother branch, was 40 mm long. The internodes were then spaced at 30 mm intervals, then 25 mm intervals, and finally the last internode was just 3 mm long, but with still developing leaves, and would have lengthened by season’s end. The penultimate internode was 10 mm long.

The leaves are alternate, meaning there is a single leaf at each node. The leaves alternate sides along the branch, because the nodes alternate sides, hence the name. (The two other leaf arrangements defined in botany are opposite and whorled.)The largest leaf on this branchlet was 90 mm long and 55 mm across the widest part. The smallest leaf was 35 mm long and 15 mm across its widest part. The very small, still developing leaves at the distal end were just 5 mm long.

The flower arrangement (inflorescence) at each node is a simple cyme. A cyme is a group of flowers in which the oldest flower occupies the end of the peduncle (the main supporting stalk, or main axis), and newer shoots come from the sides of that stalk.

As the flowers differ in age within a cyme, so too do the fruits which develop from those flowers:

And as flowers (and fruits) differ in age within a cyme, so too do they differ in age along a branchlet. Those at the fruiting mother branch (proximal) end are oldest and those at the (distal) tip are youngest. Here, these cymes which were closest to the fruiting mother branch have no flowers anymore, but do have the largest fruits. Note too the change in colour of the branchlet when moving from the proximal end towards the distal end:

The cymes at the very tip of the branchlet have the youngest flowers of all — minute buds which have only just begun development:

The cymes between these extremes occupy a gradient of mostly fruit and some flowers, to some fruit and mostly flowers, to mostly flowers and some buds, to mostly buds and some flowers. Note too the colour change along the branchlet. You can tell that the banchlet segment in the top photo below is closer to the fruiting mother branch than the segment in the lower photo below, as it is more red at the proximal end:

Fruiting branchlets are the only branches on a jujube tree to produce flowers and fruits — so writing about one allowed me to slip more botany in than I otherwise could have with another branch type!

To go further and discuss the flowers and fruits on a fruiting branchlet really require their own posts to do those topics justice. I covered Photo Journal: Anatomy of a Jujube Flower earlier, and fully intend to do one on fruit later, but here is a good place to wrap up this post with, I guess, a teaser for what will come!

The following photos are of the largest fruit on the branchlet discussed here. This fruit was the most proximal and 8 mm long.

Do revisit the flower anatomy post — this page may help too — and see if you can work out what the two little brown dots on this fruit’s distal end are. (Distal in this context refers to the end of the fruit furthest away from its point of attachment, and not to be confused with the distal end of the branchlet discussed above.)

What about now?

Yes, those are the two stigmata and the branched style of the original flower! The green fruit you see is the maturing ovary of that flower. But more on that to come later!

The proximal end of the same fruit reveals the sepal remnants:

Let’s (almost) bisect it. I say ‘almost’, as a real bisection would have had two equal halves, each with that delicate little peduncle cleaved cleanly in two along its length. Sorry but that was never going to happen!

Just looking at this you may well be able to make out which parts will become the seeds, the stone that contains the seeds, and the fruit itself? This, and what happens as the fruit grows, is definitely the topic of a future post!

Anthesis is the period or action of a flower opening, and this post will document two Ta-Jan flowers doing exactly that.

Firstly, a refresher on the parts of a jujube flower to make this easier to follow along:

 

 

Stamens and anthers are mentioned a few times in this post as, unlike the style and stigmata, they are somewhat mobile during anthesis. The stamen, the complete male organ of a flower, is not marked as such on the above photo, but is simply a word that refers to the anther and filament together. Pollen (the sperm equivalent) is produced by the anther. The filament is a stalk that attaches the anther to the flower.

You may also like to re-read Photo Journal: Anatomy of a Jujube Flower and revisit this page with the stylised diagram of a generic ‘perfect’, or hermaphroditic, flower.

Let’s begin!

Did you know jujube flowers are of one of two types? Some cultivars are morning blooming, and some are afternoon blooming. Morning blooming flowers begin anthesis in the morning, with peak nectar production that afternoon, while afternoon blooming flowers begin anthesis in the afternoon with peak nectar production the following morning.

I chose Ta-Jan flowers to photograph, as these are morning blooming. These also have a vivid yellow nectary disc! (The discs in some cultivars are less bright.)

The photos below are of the same two flowers — the top views (left) are of the same flower each time (Flower 1), and the side views (right) are of a second, same flower each time (Flower 2). The white twist ties visible were there to help me identify the same flower on the same fruiting branchlet each time — it can be hard to keep track when there are branchlets and flowers everywhere, and even more disorientating with buds turning into flowers and flowers changing form all around and all at the same time!

A flower’s bloom time is just 24 hours, but this isn’t too noticeable to a casual observer, as the flowers are both small and numerous — along any one fruiting branchlet will be many flowers representing all stages of anthesis, and a single flower tends to get drowned out in the noise! If you revisit the Photo Journal: Different Flower Stages post after reading this post, you may well see the photos on that page with new eyes, and will definitely see your own flowers in a new light!

Anthesis of a jujube flower could be broken down into several stages:

1. flower bud changes from green to yellowish
2. sepals separate
3. sepals flatten, petals and stamens (anthers + filaments) upright
4. petals and stamens separate
5. petals flatten and stamens upright
6. stamens flatten
7. nectary disc lightens

1. Flower Bud Changes Colour
Notes:
The 25th November photo for Flower 1 is more yellow in tone overall compared to the 24th November one (this is especially noticeable in the stem the twist tie is on). This is probably the camera adjusting white balance based on the more yellow bud at centre that it was focusing on. However, it’s still apparent that the bud has changed colour when compared to the smaller still developing bud to its right. (My excuse is that I’m not expert enough to adjust for white balance in the field, and it would take too long to do that in software!)

The two photos for Flower 2 are more uniform in tone, and the change in colour of the bud is more apparent. The darker background of the second image may suggest this was taken at night, but this is just an artifact of partial shadow at that time of day popping the flash. (I have everything set to auto as I trust the camera to take better photos than me — one day that will change!)

 

 

2. Sepals Separate
Notes:
The more yellow hue of Flower 1’s sepals is more evident here, when compared to the buds to its right.

 

 

And here’s Flower 1 a little later, at 9:59am:

 

 

3. Sepals Flatten, Petals and Stamens (Anthers + Filaments) Upright
Notes:
The glistening you can see on the nectary disc of Flower 1 is nectar production. You may just be able to see the bright yellow disc on Flower 2 too.

If you look really closely, and compare this photo immediately below to the very first photo at top of page (’Jujube flower anatomy’), you’ll note that the petals and stamens here appear combined. The stamens’ filaments are actually tucked into the ‘handle’ part of the little green spoon-like petals — and once you know that you might be able to make out the anthers as the whitish, pointed tips that extend from the ’spoon bowl’ part of the petals further back. The next photo will make this clearer.

 

 

4. Petals and Stamens Separate
5. Petals Flatten and Stamens Upright
Notes:
Here the petals are now in the same plane as the sepals while the stamens remain upright, the whitish anthers shining like little beacons atop the green filaments. The nectar produced by the nectary discs of both flowers is already attracting ants.

 

 

6. Stamens Flatten
Notes:
I missed when this actually happened for Flower 2, but the photo of it the morning after still makes the point!

 

 

7. Nectary Disc Lightens
Notes:
The nectary disc lightens as anthesis progresses, to become the same colour as the sepals:

 

 

To wrap up, here’s a photo of Flower 1 and some neighbours, just to illustrate how as some flowers advance through anthesis, others are at their end of life (perhaps having never been pollinated), others are just beginning, and attracting pollinators, and others still are yet to move from the bud stage:

 

 

And this is along just two centimetres of one fruiting branchlet!

For a bit of relaxing quiet time, why not grab a magnifying glass (or loupe if you have one) and peruse your own flowers? You may even enjoy watching pollinators moving about — hopefully pollinating as they go! Speaking of pollination, ongoing flower evolvement post-pollination into fruit development is another post I will be covering in due course!

Back here were lots of pretty pictures of jujube flowers, but not exactly much in the way of information as to what you were looking at.

As with that week, this week is another time-poor one I’m afraid. But while this post will also be photo-heavy, it won’t be as light on the words, and you may even be tempted to wander outside to examine your own flowers (jujubes or otherwise!) by the end of it!

Let’s first look at a stylised diagram of the parts of a flower. The flower in that illustration is a perfect flower — to botanists, that means it’s a bisexual or hermaphroditic flower, with both male and female organs, and able to reproduce on its own. More specifically, a perfect flower is one that:

1. makes and distributes male gametes (male sex cells, or pollen, the equivalent of sperm in animals)
2. makes female gametes (female sex cells, or ovules, the equivalent of unfertilised eggs in animals)
3. receives male gametes (pollen) able to fertilise the female gametes (ovules)

The third point is crucial as it is this capability that makes a perfect flower able to fertilise itself (though often with the help of pollinators such as insects or birds). Making male and female gametes is one thing, but if an ovule can’t then receive the pollen from its own flower, then that flower cannot fertilise itself.

I’m mentioning all this of course, because jujube flowers themselves are perfect flowers. Here’s a close-up of one. With reference to the stylised diagram, can you pick out the sepals, petals, anthers, filaments, bifurcated (branched) style and stigmas/stigmata (plural forms for stigma) in the jujube rootstock flower below?

(What you may think is the ovary is actually a nectary disc, which is above the (covered) ovary. See how it glistens with nectar?)

Here’s a different angle, of a Chico flower (this one’s nectary disc has finished secreting nectar):

How’d you go?

Probably the trickiest part is distinguishing those ever so tiny, delicate spoon-like petals from the petal-like sepals! You have to really look hard to notice them. And you have to look harder again to even notice the tiny anthers and filaments, which practically merge into the background and look like part of the petals at a casual glance.

It’s the sepals we see folded into the distinctive pentagonal shape of the flower buds:

And there you have it, the anatomy of a jujube flower — you’ll never mistake sepals for petals again, will you?!

And so as not to leave you hanging, here is a spent flower with the nectary disc and now visible ovary:

Rather than a post last week, we had threee guest comments under this older post — direct links are here, here and here — and a big thank you to Adrian and Airlie for sharing their experiences! I stupidly didn’t actually post those links publicly at the time, and only subscribers were notified unfortunately. This post hopefully rectifies that mistake.

The past few days have been…quite full (!) of late with my advanced heirloom tomato plants, and now I find myself a day late in getting the regular post out!

I was intending to follow up on my comment in that older post, but this week because of time thought a quicker post of flower photos might still be of interest. Every fruiting branch, when covered in flowers, has flowers at all stages, from newly-formed bud to open-and-ready-for pollination. This is why jujube trees have an extended cropping period that lasts weeks to months.

This one is my absolute favourite, taken by my sister-in-law some years ago now. It shows an ant pollinating an open flower, with very new budding flowers nearby:

The photo above best gives you an idea of scale too. The new buds would be 2 or 3mm across while the pretty five-pointed stars that are the fully opened flowers vary from about 6 to 7 mm diameter, depending on the cultivar.

Other photos in no particular order: