Botany marches on – Part 1, basal angiosperms and monocots

April 13, 2010

Warning! I’m going to get into some detailed botany here, so if you are not deeply into the flowering plants and their classification and you do not own my book, A Tour of the Flowering Plants, you may not wish to wade through all this. It is basically for advanced elementary and secondary Montessori botany studies and for anyone else that owns the book. A Tour of the Flowering Plants is still quite useful to show the appearance of angiosperm families, whether or not you are concerned about the latest classification.

Last fall, the Angiosperm Phylogeny Group published a third report concerning the classification of the orders and families of flowering plants. The report, published in the Botanical Journal of the Linnean Society, is called APG III. There is a summary of APG III on Wikipedia. http://en.wikipedia.org/wiki/APG_III_system My book, A Tour of the Flowering Plants, is based on the 2003 report from this group, which is called APG II. The book has some further advances that were published on the Angiosperm Phylogeny Website of Peter Stevens. http://www.mobot.org/MOBOT/Research/APweb/welcome.html

I’ll go over the APG III changes, beginning with this post. If you own my book, you can decide if you want to add notes to it. You may contact me via my website (www.bigpicturescience.biz) if you would like a list of the pages and changes for bringing A Tour of the Flowering Plants in line with APG III.

Will the changes keep coming over the years as we acquire more and more DNA data? I think that future changes will be modest and will not affect the general structure of the angiosperm tree. There aren’t that many unplaced groups left. There will likely be little surprises, like one I give below for Nymphaeales.   

For now, let’s start with the first branches of the angiosperms, grouped as the basal angiosperms in A Tour of the Flowering Plants. The Nymphaeales got another family, Hydatellaceae, which was formerly placed in the grasses. This shows how much DNA studies can reveal, and what studies of morphology may not be able to distinguish. This family is tiny, both in size and numbers of species. The only reason I mention it is the idea that when plants adapt to living in water (or any other extreme environment), they often change form so much that they don’t resemble even their closer relatives. You can see the plant here: http://www.ubcbotanicalgarden.org/potd/2007/03/hydatellaceae_1.php

The order Chloranthales was previously unplaced – no one was sure what its closest relatives are. Now it is considered to be a sister group to the magnoliids. The magnoliids themselves have not changed in APG III. This branch of the flowering plants includes the laurel and black pepper families, as well as the magnolias. Although their seeds have two cotyledons, they are not closely related to the eudicots. The eudicots are the traditional dicots minus the magnoliids and the basal angiosperm lineages.

In A Tour of the Flowering Plants, I used terms for branches of monocots that have since disappeared. You don’t have to worry about whether to call the Liliales and Asparagales “lilioid monocots” or “petaloid monocots.” Just call them monocots and go on. The only lineage of monocots that gets a special name now is the commelinids. “Lilioid” and “petaloid” should be understood as informal terms that refer to plants that were traditionally lumped in the lily family. Most of them have large, showy tepals.

The major change in the monocot is the grouping of several small families as subfamilies under the enlarged families Amaryllidaceae, Asparagaceae, and Xanthorrhoeaceae. This is all within the order Asparagales. Here’s the breakdown:

The enlarged Amaryllidaceae has the agapanthus subfamily (Agapanthoideae, equivalent to the former Agapanthaceae), the onion subfamily (Alliodeae, equivalent to the former Alliaceae), as well as the amaryllis subfamily (Amaryllidoideae, equivalent to the former Amaryllidaceae). The members of this enlarged family have their flowers in umbels that are enclosed by two bracts when the flowers are in bud.

The enlarged Asparagaceae is really big. It has the Brodiaea subfamily (Brodiaeoideae), the scilla subfamily (Scilloideae, which includes the former hyacinth family, as the tribe Hyacintheae), the agave subfamily (Agavoideae, which includes the former Agavaceae), the Nolina subfamily (Nolinoideae, equivalent to the former Ruscaceae), as well as the asparagus subfamily (Asparagoideae). Yet another subfamily holds several Australasian species such as the cabbage tree, Cordyline.  

Asparagaceae members have flowers in racemes or in umbels that have three or more bracts at their base. The umbels, if present, do not have the pair of enclosing bracts seen in Amaryllidaceae.

The enlarged Xanthorrhoeaceae (the grass tree family) includes the daylily subfamily (Hemerocallidoideae) and the asphodel subfamily (Asphodeloideae), as well as the grass-tree subfamily. I did not include the grass tree family in A Tour of the Flowering Plants because it is native to Australia and not commonly used in North American landscaping.

The cattail family, Typhaceae, got a second genus, Sparganium, the bur-reeds. It’s not hard to see these two aquatics as relatives.

I’ll address the APG III changes to the eudicots in another post.


Pollen cones

April 13, 2010

I was so concerned with getting the photos of the seed cones (ovulate cones) into my last post that I forgot to show the pollen cones of the ponderosa pine. Here are a couple of views.

The young pollen cones of the ponderosa pine.

 

One pink seed cone and many pollen cones ready to release their pollen.


A pine cone tale

April 7, 2010

A major goal of Montessori botany studies is to help children learn to observe and understand plant structures. There are a lot of things going on in the plant world that take a sharp eye and careful observation to find. The life cycle of pines is one of them. It is important for the teacher/guide to show children inconspicuous plant structures such as pine cones throughout the year and explain to them what is happening.

Most people are familiar with conifer cones, although they tend to call all of them “pine cones.” Few have followed the development of a cone through the year – or two years in the case of pines – that it takes for a cone to mature. I have been photographing the development of pine cones and here’s a look at their life cycle.

Pines have two kinds of cones on the same tree, pollen cones and seed cones. The latter are formally called ovulate cones. The trees don’t usually form cones every year. In cone years, the cycle begins as the new shoots elongate in the spring. The seed cones form at the end of the new growth. They look like tiny pink-to-purple bristles.

These are young seed (ovulate) cones on the new shoot of a ponderosa pine.

The pollen cones cluster at the base of the new shoots, beneath the terminal bud. Most of the pollen cones form on the lower branches of the tree, away from the seed cones, but sometimes they form on the same shoot as the seed cones. The wind usually won’t take pollen from the base of the tree to its upper branches, so the arrangement of seed and pollen cones encourages cross-pollination. 

These two cones formed in the previous spring. The one on the right died during the winter. The left one is starting to grow.

  

By early July, the living seed cone has quadrupled in size. Its scales are noticeably green.

Conifers use wind pollination, which requires a lot of pollen to work, and in cone years the trees produce an amazing amount of pollen. Pollen cones tremendously outnumber seed cones. After they release their pollen, most of the spent pollen cones drop off the tree. You can sometimes find dried ones in the branches later in the summer, however.

It takes careful observation to find the budding ovulate cones, even though they can be colorful. They hide among the new needles and are most easily seen from above, the bird’s eye view we don’t usually have. It doesn’t help that the ovulate cones usually form on the higher branches. You may need to pull a branch down so that the children can see the tiny new cones. The little cones of pines don’t grow much during their first year. In the fall, they have become browner and drier looking, but are nearly the same size as they were in the spring.

In the second spring the pine seed cones rapidly enlarge. A shoot I photographed had a pair of seed cones, but one of them had died. It provides a size scale to show how much the live cone has grown. Fertilization is a slow process in pines. It takes about 15 months for the egg cells to form and the pollen tube to grow and deliver the sperm to the eggs. The scales of the seed cones are green until late fall. By that time the seeds are mature. The cone dries and the scales spread apart, releasing the winged seeds. The dried cone may remain on the tree for months or years, until a strong wind brings it down.

In the fall, the seed cone has dried. Its brown scales spread apart and the seeds are released.

In case you need help finding your local pines, look for a conifer tree with needles in bundles of two to five. Other conifers, such as firs or spruces bear their needles singly. Their cones mature in one year, but they can be even harder to see because the seed cones form in the tops of the tree.

Take a look around this spring and see if you can locate some young cones to show your children and to follow through the cone life cycle.

The winged seeds of the pines blend in with the soil and rocks very well.


Blooming trees that are hard to see

March 21, 2010

Happy equinox and happy tree watching!! Some trees in your area may have already bloomed, and others may be still to come. Some trees put on such a lovely show that no one can miss their blooms. For others, it takes a sharp eye and sometimes a hand lens to see the blooms. I’d like to show you the details of a few of them. For this post, I’ve chosen ash and elm trees.

Elms, genus Ulma, have their own family, Ulmaceae, which is part of the Rosales order in the rosid branch of flowering plants. They are very early bloomers, and as a result they may have their blooms frozen. If they are able to form fruits, these grow before the leaves. The trees have an early display of “spring green” fruits, which then turn brown and blow away as the new leaves are emerging.

The staminate and pistillate flowers of Siberian elms open while the weather is still freezing.

What’s the advantage in blooming so early and risking a late frost? These trees are wind-pollinated. The leaves would block the wind from the branches where the flowers form. Instead the trees take the risk and produce large numbers of fruits (“elm seeds”) as a trade-off.

The flowers of elms are tiny clusters of staminate and pistillate flowers that have tiny tepals, not showy petals. The stamens have dark anthers and the pistillate flower has two tiny, furry stigmas, usually light-colored. The ovaries start to enlarge soon after the trees bloom, and you can see the enlarging green disk that will become the fruits.

The samaras of elms grow quickly and mature before the leaves open. This is a Siberian elm.

The fruit is known botanically as a samara, which literally means “elm seed” in Latin. A samara is a winged fruit that is wind-dispersed. Elm fruits have a single seed surrounded by a membranous ring.

The flower clusters of the American elm are more open. Each flower has a long stalk.

 

The developing ovaries of the American elm are covered with short hairs.

Ash trees, genus Fraxinus, belong to the olive family, Oleaceae, which is part of the Lamiales order in the asterid branch of flowering plants. They bloom later than elms, but still quite early. Ash trees are dioecious, which means that they have their staminate and pistillate flowers on separate trees. The staminate or male trees are often planted as street trees. They have the advantage of not producing fruits, so not requiring a lot of clean-up. Their distinct disadvantage is that they produce abundant allergy-triggering pollen.

The staminate inflorescences bear two stamens per flower, like all the olive family. They start as tight, globular clusters. The more open inflorescences of pistillate flowers show the tiny green ovaries that rapidly enlarge. The fruits are another samara.

Early on, the immature stamens form tight clusters as they emerge from their buds.

Later the stamens mature as the cluster opens. The pollen flies as the anthers split open.

This pistillate ash tree has the old, dried fruits (samaras) from the previous year, along with the green inflorescence of this spring.

  


Poinsettia flower hide-and-seek

December 4, 2009

Poinsettia plants (Euphorbia pulcherrima) have become a traditional winter holiday decoration. If you have one available, try to find its flowers. It isn’t an easy task. While every species of flower is a variation on the basic theme of flower parts, the poinsettia and other members of the euphorbia family are particularly unusual.

First, I should define what I mean by a flower. Botanically it is the reproductive structure of a flowering plant. A “complete” flower – one that has all the usual parts – has a calyx made of sepals, a corolla made of petals, stamens, and a pistil. Not all these parts are necessary for the flower to function – that is, to make a fruit and seeds. To be a flower, the minimum requirement is at least one stamen or one simple pistil (carpel). All those other structures just enhance the function of the stamen or the pistil. The stamen produces pollen, which holds the sperm cells that will fertilize the egg cell and endosperm in the ovule. If the ovules are fertilized, the ovary of the pistil matures into a fruit with seeds inside.

If you want to figure out the poinsettia’s flowers, it really helps to see the developmental sequence. Poinsettias are usually sold when the flowers are fully formed, so I’ve provided some photos of earlier stages to help you see what’s what.

In mid-October, these poinsettia plants are all green. They haven't started forming bracts.

First, let’s take a look at the parts are NOT flowers. Hint: look for the most conspicuous and showy parts. The colorful petal-like parts are simply modified leaves that help attract pollinators. They are called bracts, and they develop when the days are short in the fall. The photo

Only ten days later, red bracts are starting to form.

sequence of poinsettias in a greenhouse shows that the bracts are leaves that are colored. Bracts have the same vein pattern as leaves and if you look at the stem, you will see that they have an alternate arrangement – one bract at each node – instead of the whorled arrangement that petals usually have. 

The bracts have an alternate arrangement on the stem - one per node.

 

Look at the photo below that shows a cluster of small green rounded structures in the center of the bracts. Are they the flower buds? No, they are developing inflorescences. An inflorescence is a group of flowers on a single stem. The botanical term for this inflorescence is a cyathium, which comes from the Greek term for a cup. As these structures mature, they become cup-shaped. The rim of the cup takes on a color, yellow to red, depending on the variety. One or two structures that look like yellow or orange lips grow on the top of the cup. While most nectar glands are in a single flower, these reward pollinators for visiting the whole inflorescence.

The little green structures in the center are the early stages of the inflorescences, the cyathia.

Each cyathium holds either stamens, a pistil, or a mixture of them both. Normally when you see stamens and a pistil, you are looking at parts of one flower. Here each individual stamen or pistil is a separate flower with its own separate stem. You can see this most clearly on the pistils. Their stems elongate and push them out of the cyathium as they mature. Many of the poinsettias sold commercially seem to have only staminate flowers. You can see the dusty yellow pollen on the anthers at the ends of the filaments. The pistils are three-carpellate – composed of three fused carpels (aka simple pistils). The style of each carpel curls open and splits in two as it matures. When the pistil first forms, you may see only the styles and stigmas. As it grows, you can see the whole ovary and its stem hanging out of the cyathium.

These cyathia have only stamens. Note the yellow anthers and red filaments. The yellow nectar glands are near the top of the cups.

In this variety, the styles and stigmas are red. The stamens are yellow. The pistils have three styles that each split in two.

Even if your poinsettia has pistillate flowers and its ovary grows, don’t expect seeds. Most hybrids with those large colorful bracts are no longer fertile. They are propagated from cuttings. Poinsettia growers seldom grow plants from seeds. If they did, they would get a range of bract colors and maturity times, rather than all the plants looking the same. In fact, poinsettia seeds are hard to find. I found only the wild type in a recent search.

The ovaries of the pistillate flowers have enlarged. Their stems have pushed them out of the cyathia.

After your poinsettia has bloomed, the bracts remain even as the cyathia drop off. You can keep it and allow it to grow. In the spring you should cut back the bracts to keep the stems from becoming long and scraggly. This allows new leaves to form. If you want the plant to form bracts and flowers again, it will have to be kept in the dark for about 15 hours a day until the bracts are colored. For more information, see http://aggie-horticulture.tamu.edu/extension/newsletters/hortupdate/novdec00/art1nov.html  

Poinsettias are rumored to be poisonous. They certainly should NOT be considered edible, but their milky sap is only mildly irritating. Finally, my thanks go to TaTonka Farms of Conifer, Colorado for allowing me to photograph their beautiful poinsettias throughout the growing season.  Happy holidays!

This variety has variegated bracts.


Seen any good grass flowers lately?

July 10, 2009

Our summer is rushing along, as summers usually do. With the abundant rains this year, grasses are growing profusely and the grass flowers have been a treat to see. If you ask most people, they will say that grasses don’t have flowers. It all depends on what you consider a flower. The common notion is that a flower has to be colorful and showy. That’s fine if the flower is pollinated by an insect or other animal, but wind-pollinated flowers don’t bother with all that extravagant use of resources. Their flowers are the most basic models – tiny petals or none at all, no scents, no nectar. The wind doesn’t work any better with those things than it does without. All it takes to be a flower is a stamen or a carpel, and grass flowers have both – one to three stamens and a two-carpellate pistil usually.

Here are typical grass flowers. The anthers are yellow and the stigmas are feathery and white.

Here are typical grass flowers. The anthers are yellow and the stigmas are feathery and white.

I’ve been asked what grass flowers look like, and that’s a good question. Without a hand lens or other magnifier, it is hard to see them at all. Basically grass flowers form within a series of bracts – small modified leaves, which are usually green. This little package of flowers and bracts is called a spikelet. Each spikelet can have one to several flowers + bracts stacked together. When the flower is mature, a pair of little scales (the lodicule) at the base of the ovary swells and prys the stack of bracts apart. The stamens, typically three of them, dangle out on long, flexible filaments. The anthers are large compared to the size of the whole flower. They have to be to shed enough pollen. Wind tends to scatter pollen and dilute it. The stamens are the easiest part of the grass flower to see. The pistil typically has two styles and two feathery stigmas. If you would like more details on grass flowers see http://www.backyardnature.net/fl_grass.htm

The feathery stigmas have a large surface area to snag pollen. Their structure may also alter air flow, making it more turbulent and promoting pollen contact with the sticky stigmas. The stigmas are often white, but there are many colors in various grass species. After the grass flower has bloomed, the bracts close back up and there is little of the flower to see on the outside of the spikelet. Sometimes the stamens remain for a short while after the bracts close. Inside, the ovary of the flower is developing into a closed, dry fruit. The layers of the ovary wall adhere closely to the seed, so the whole thing is commonly called a seed or a grain. A kernal of wheat, for example, is technically a grass fruit.
This switchgrass has orange anthers and pink stigmas - pretty fancy for a grass.

This switchgrass has orange anthers and pink stigmas - pretty fancy for a grass.

The grass family is one of the largest of the flowering plant families, so my photos show only a tiny fraction of the variety of grass flowers. It’s another good challenge for field work – find the grass flowers. Happy hunting!

Many flowers in this grass inflorescence are blooming. 

Many flowers in this grass inflorescence are blooming.


Postscript on slime molds

June 24, 2009
My tomato plant has a slime mold!

My tomato plant has a slime mold!

Slime molds seem to be traveling lately. For the first time, one of them appeared in a pot in my greenhouse. I was away for a few days and didn’t catch it in the act of crawling up on the side to form its spores, but there it is. I wonder if I brought the spores into the greenhouse on my hands or clothing after I found (and poked) the one under the juniper tree.

Once my cucumbers had mushrooms, a species that is considered a pest in greenhouses. I suppose it shows that fungi and slime molds spread themselves far and wide, like other organisms that depend on tiny spores for reproduction. Once in a while a spore lands in a good place to grow and that makes up for the huge numbers of spores that don’t grow into anything.