Just a bit earlier in the series, we introduced the angiosperms, which are the flowering plants.
This is an incredibly diverse clade that includes everything from asparagus to apples, from
clovers to cacti, from oil palms to potatoes, from maize to mistletoe, and many others.
So now it’s time to dive into that diversity so we can further classify them.
Angiosperm evolution is complicated, and it’s possible that our current classification may
be rewritten someday.
However, current cladistical modeling indicates that they can be broadly separated into “basal”
and “core” groups.
The basal angiosperm clade is paraphyletic, meaning that it includes the most recent common
ancestor of all the organisms, but does not contain all of the descendants of that common
ancestor, as opposed to being monophyletic, which would mean that it does contain all
the descendants of the most recent common ancestor.
The basal clade contains only about 175 species that diverged early on in angiosperm evolution.
The basal angiosperms include the Amborellales, a monophyletic order of small shrubs, the
Nymphaeales, an order of aquatic plants, such as the water lilies, and the Austrobaileyales,
an order of woody trees, shrubs, and vines such as star anise.
The core angiosperm clade, also known as the mesangiospermae is monophyletic and includes
over 99.9% of all flowering plants.
They are further divided into five clades, the ceratophyllales, chloranthales, magnoliidae,
monocots, and eudicots.
The clade ceratophyllaceae is a cosmopolitan family, meaning it is found all over the world,
and it includes a single extant genus of aquatic flowering plants commonly known as hornworts,
where extant means still in existence today.
The clade chloranthaceae is a family of woody plants found in many tropical regions around
the world and often used in traditional medicines.
Now, it might seem like I’ve already covered a lot of angiosperm diversity.
However, the five clades I’ve just mentioned, though evolutionarily distinct, account for
only about 0.1% of known angiosperms.
The clade magnoliidae makes up another 2% of all known flowering plants.
This group of plants includes species that are economically important for food, drugs,
perfume, and timber.
They include some more widely cultivated tropical species like the avocado, black pepper, cinnamon,
and soursop.
They also include the ornamental magnolia trees, the laurels, and others.
So that leaves us with just two clades left to cover, the monocots and the eudicots.
These two clades make up almost 98% of all flowering plants and are the two groups most
commonly discussed in angiosperm classification.
Their names refer to the first embryonic leaves, or seed leaves, that appear on the plant embryo.
These are also called cotyledons.
A monocot embryo has a single cotyledon while a eudicot has two cotyledons.
The monocots account for about 60,000 species, which make up roughly 23% of all named angiosperms.
The largest family of monocots, by far, are the orchids, which account for about 20,000
to 28,000 accepted species.
Orchids alone represent about 6-11% of all seed-producing plants.
Though orchids are often thought of as tropical species, and it is true that their diversity
is greatest in the tropics, they’re actually found on every continent except Antarctica.
Other major groups of monocots include the bamboos, palms, lilies, and grasses.
The majority of the biomass produced in agriculture comes from the monocots.
This is because all major grains, like rice, wheat, maize, barley, millet, and oats are
monocots.
The same goes for all forage grasses, which are used as feed for cattle, along with sugarcane,
bananas, gingers, pineapples, leeks, onions, and garlic.
In addition, many bulb plants cultivated for their blooms, like bluebells and tulips, are
all monocots.
Moving on, traditionally the angiosperms had been separated into two groups, the monocots
and the dicots.
This is because monocots have many distinctive features that separate them from dicots.
For example, monocot leaves usually have parallel veins, while dicot veins are usually branched.
Monocot stems have vascular tissues arranged in a complex array of tiny bundles throughout
the stem, while dicot stems have their vascular bundles arranged in a ring.
The petals of monocot flowers are generally arranged in multiples of three, while dicot
flowers are generally in multiples of fours or fives.
Finally, the roots of monocots form a fibrous system, like a mat of threads that spread
out below the soil surface.
Dicot roots, however, have a large vertical taproot that burrows deeper into the soil.
However, this simplified two group system has since been abandoned.
Although all of those characteristics are still unique to the monocots, the old classification
of “dicot” has since been split up into the basal angiosperms and magnoliidae that
were mentioned earlier, and the eudicots or “true” dicots.
The eudicots make up about 75% of all flowering plants.
They are all evolutionarily related and distinguished from all other flowering plants by the grooved
tricolpate structure of their pollen.
All other angiosperm groups produce monosulcate pollen, with a single pore set in a groove
of a different orientation.
Some botanists prefer to call the eudicots “tricolpates” in order to avoid confusion
with the old dicot classification.
However, since they’re more commonly referred to as eudicots, we can stick to that here.
The eudicots include most shrubs and leafy trees, along with the carnivorous plants,
many ornamental flowers, and a huge range of food crops including most fruits, vegetables,
and nuts.
Apples, coffee, pumpkins, celery, cannabis, nightshade, oaks, maples, corpse flowers,
eucalyptus, aspen, dandelions, oranges, buttercups, morning glories, cacti, cherries, cranberries,
carnations, and so many other plants are all classified as eudicots.
This clade includes a truly staggering amount of species that have adapted to unique habitats
all over the world, from the hottest deserts, to some of the coldest tundras, and everywhere
in between.
Perhaps we will take a closer look at some of these species a bit later in the series.
But for now, that completes an introduction to a general classification of the most diverse
extant group of plants, the angiosperms.