Sunday, March 22, 2020

Why are Anthuriums red?

One of my favorite plants is this cultivar of
Anthurium andreanum, with spathes of
pure, bright red. If treated well, it will bloom

More correctly, the title of this post should read "why are the spathes of some species of Anthurium red?' - but that's way too wordy for a title.  The fact of the matter is that there are some 1000 species of the genus Anthurium, and only a few species have red spathes.

The most commonly cultivated species is Anthurium andreanum, available in many different cultivars and hybrids. It is native to Ecuador and neighboring Columbia. Little is known about the species reproductive biology in the wild, but the bright red spathes literally scream "birds!" Well, not quite literally, but bright red colors in plants usually are an adaptation for attracting birds, either for pollination or fruit dispersal.

It has been speculated that the red to orange spathes in wild plants help birds find the ripe fruits, which they would eat, fly off, and thereby disperse the seeds. It's a common dispersal adaptation, found even in the most archaic of angiosperms (e.g. Amborella), and it may very well be true in this species, as well as many other species of Anthurium.

In all members of the Aroid family, flowers are tiny and crowded onto the elongate spadix.  There have been many observations of pollination by tiny flies, beetles and other insects in various species of Anthurium, and it has been assumed that birds would take no notice of them. That was until recently.

A 2019 article by Bleiweiss et al. provides the best evidence so far for bird-pollination in Anthuriums with red or other brightly colored spathes. It wasn't the first evidence of the possibility, as Bleiweiss cites a paper from some 20 years earlier by Kraemer and Schmitt making similar, if not as thorough, observations.

This reminded me of seeing nectar drops on an Anthurium andreanum specimen in the Bailey Hortorium greenhouse at Cornell, some 50 years ago, and wondering the same thing.  That picture is posted below. You can see the nectar exuding from several of the tiny flowers.  A patient hummingbird could get a decent meal by collecting a series of these droplets.

Makes me think about some other pollination mysteries ... stay tuned.
Anthurium andreanum growing in a greenhouse at Cornell University around 1970. note the tiny droplets on some of the upper flowers (enlarged below).

Friday, March 13, 2020

Plant wrappers - leaf sheaths and bracts

While the young leaves of Magnolia
are developing,  they are each wrapped in a white
bract (technically a specialized, bract-like stipule).
Leaves are the most plastic of all plant organs.  That means that they can be modified in endless ways
to result in a mind-boggling variety of shapes. Through evolution via adaptive modification, leaves form an endless array of light-gathering antennas, from the giant fronds of palms to the tiny scales of a juniper twig, but beyond that, have adapted into tendrils, insect-catching traps, and even the parts of the flower.

In the fennel plant, the broad basal portions
of the leaves, the leaf sheaths, overlap to protect
the developing shoot apex.
Today, I'm talking about leaves, or parts of leaves, that form wrappers around tender growing parts of the shoot.  Modified leaves that do so are called bracts, and the modified lower parts of leaves that do so are called leaf sheaths.

A bract is a whole leaf, though it is typically smaller than a regular leaf, simpler in shape, and often colored differently. In some cases, brightly colored bracts serve as part of the apparatus for attracting pollinators, and may even appear to be petals.

A leaf sheath, on the other hand, is the broad basal part of typically large, complex leaves that surrounds the growing tip of the shoot. The rest of the leaf - typically a petiole and a blade - is typically full-sized,

As flowers and leaves emerge from a Crocus corm
in early spring, they are protected by white bracts.

In this bromeliad, Tillandsia cyanea, a fan of colorful
bracts help keep the plant on the radar of pollinators
as the flowers emerge one at a time.

Pachystachys lutea, or yellow shrimp plant, forms
a cone of yellow bracts to attract pollinators to
the white flowers.

As for leaf sheathes, some of the most spectacular are found in palms, but virtually all monocots form a leaf sheath when young.  Leaf sheathes attach to the stem in a complete circle when young, but typically splits apart on one side as the leaf matures and the stem within it expands.  In others, such as the royal palm, the overlapping leaf sheaths of the functioning leaves remain as a smooth, tight, crownshaft.

The leaf sheathes of the royal palms (Roystonea spp.) can be more than  four feet long.  They remain intact as complete
cylinders, forming what is called a crownshaft.  Photo from Palmpedia, photographer not indicated.

The "trunks" of banana plants are made up entirely of leaf sheaths, that may be more than three meters long, wrapped around each other (see "The invention and reinvention of trees")
As each new leaf emerges from the tip of the shoot
of a banana plant, its sheath is longer than the previous
ones.  This builds up a pseudostem of overlapping,
cylindrical  leaf sheaths.

Recall from "The underground plant movement" that the bulb of an onion or amaryllis is also made up of leaf sheaths that fill up with food and water, and are left as storage organs as the leaf blade on top of them dries up and disappears.
In a young onion plant, the leaf sheathes just above
the roots begin to fill with food.

When the onion plant goes dormant for the
season, the food-filled leaf sheathes remain,
forming  the rings of the onion.  The
outermost sheaths dry out to form a
protective tunica.
In many irises, gladioli and other members of the
Iridaceae, the leaf sheath is folded and the entire
shoot looks like it has been pressed with a hot iron.
Note that the newer leaves emerge from the
overlapping, folded leaf sheathes.

Friday, December 6, 2019

Good fire, bad fire

sometimes seems that all wildfires are bad.  Forests burn down, homes and whole towns are destroyed, carbon dioxide is released into the air, valuable wood is destroyed, and wild animals are killed or driven from their habitat..

So it is surprising to hear for the first time that wildfires are natural and necessary in many ecosystems.  They become bad basically only because of our own interference.

As in many pines, the seed cones of  Banksia in
Australia, open only after a fire to release their
Ecosystems in which fires are a normal part of maintenance or renewal are those in which there are distinct wet seasons and dry seasons.  During the wet season, there is abundant growth of trees, shrubs, grasses, and other herbs  During the dry season, leaves and twigs fall from the woody plants and grasses dry out.  Typically, this debris accumulates faster than it can decay, so builds up from year to year.  Sooner or later a lightning strike will ignite the accumulated debris, causing a wildfire.

 Burning removes the debris, releases nutrients back into the soil, clears out the undergrowth, trims dead branches from the trees.  In some cases, shrubs are burnt to the ground, but re-sprout quickly at the beginning of the next wet season.

Plants in these areas are adapted to these periodic fires. Pine trees, for example, survive moderate fires, and require the ground to be cleared for seeds to germinate.  In many species, seed cones will not even open until heated by fire.  Where fires are prevented for a number of years, ground vegetation becomes thick and pines do not reproduce, and when fire inevitably strikes, it is more intense and trees die.  For these reasons, foresters often conduct regular controlled burning to prevent more intense fires later.

In the pine flatwoods of Florida, fires remove the undergrowth and debris, clearing the way for 
germination and growth of pine seedlings.  Without fires, pines would gradually disappear.  
Their thick bark protects the trunks, and the upper branches are spared as well, as long as fires  
are frequent and not too intense. Saw palmettos, Serenoa repens, cover much of the ground  
here, but can be seen here recovering quickly after a fire.  
Bulb plants, like this Florida native Lilium catesbaei,
survive fires below ground.  Plants that sit out
the dry fire season are particularly common in
California, South Africa, and Australia.

The California chaparral and other forms of Mediterranean vegetation are adapted to winter rains and long summer droughts, and are also fire-maintained. It is here where we see shrubs well-adapted for re-sprouting after burning to the ground.  Grasses, and wildflowers also thrive after fires, and are suppressed if the shrubby overgrowth becomes too thick.  Between the pine forests and the chaparral, much of California is thus prone to natural fires, setting up an unfortunate conflict between nature and people building homes on vegetated hillsides.  The same tragic conflict can be seen in many parts of Australia and southern Africa.

Wildflowers, such as this Liatris, flourish where
fires are frequent in Florida.

The only places where wildfires are rare are in areas with reliable, year-round rainfall, or in areas of practically no rainfall.  So rain forests, temperate deciduous forests, and deserts do not normally experience fires.  In the rain forest, and temperate forests with precipitation all year long, vegetation rarely dries out, and debris is decomposed quickly.  In the deserts, vegetation is sparse, and very little debris is produced. It's the areas between these extremes that rely on fires.  Aside from the chaparral and pine forests mentioned above, this would include the grasslands and deciduous tropical forests that cover vast areas of Africa and tropical America.

So how do we humans turn good fires into bad fires?  There are several ways.

First, by overzealous prevention of fires where fires should normally be occurring, we allow more debris to build up, allow opportunistic undergrowth vegetation to run rampant, setting up for a more disastrous fire when lightning eventually strikes.  In these disastrous fires, pines are not only pruned, but burned to the ground.  Such fires may be so hot that even the root systems of normally resilient shrubs are destroyed, and then do not re-sprout.
After the big fire in Yellowstone National Park in 1989, grasses and wildflowers, such as the pink fireweed, Epilobium angustifoliumgrow abundantly, a boon to local herbivores. 

Second, climate change is resulting in the expansion of dry seasons into formerly wet forests in many parts of the world. The intensity of droughts, as well as floods, hurricanes, and blizzards is increasing. This is not currently seen as a significant factor in the catastrophic fires in the Amazon Basin, but are a factor in the desertification of the African savannas.

Third, clearing and burning of forest for conversion to farm or grazing land, which is occurring in the Amazon Basin at an increasing rate, can get out of hand during dry periods and burn more extensive areas than normal. Fires are normal only where rain forest transitions into deciduous tropical forest, mostly along the southern fringe of the Amazon forest. Clearing of the forest, apparently supported by the current government, is also fragmenting the forest, causing it to get drier and less able to sustain itself.

So the burning of the Amazon rain forest, unlike the routine burning of the chaparral and pine forests, is a tragically bad fire.  It is resulting in a significant loss of biodiversity and loss of photosynthetic activity that could help offset climate change.
Rauch steigt in Brasilien auf - die Feuer haben sich in den vergangenen Tagen ausgebreitet
The fires in the Amazon Basin are largely due to human activity.  They are a tragedy because of the huge loss of  biodiversity, release of CO2 into the atmosphere, and loss of photosynthetic oxygen replenishment. 

Wednesday, September 25, 2019

Pitfalls of the long branch

Long branches in phylogenetic trees represent lineages of  organisms that have been around for a long time, but exist today as only one or a few species.  A few years ago, I discussed two examples in detail: the monocot genus, Acorus, and the archaic angiosperm species Amborella trichopoda.  I feel that the topic is worthy of a review, especially for newer readers who may not have gone back to the older posts. 

In both cases, these lineages branched off very early, over 100 million years ago, but have left no fossils, and have no close living relatives.  The Amborella branch is the earliest surviving lineage of angiosperms in general, while the Acorus branch is the earliest surviving lineage of monocots.  Expressed in a different way, Amborella is the sister group to all other angiosperms, and Acorus is the sister group to all other monocots.

At the level of phylogenetic analysis, such long branches have often been problematical, with "long branch attraction" leading occasionally to errors in the resulting phylogenetic tree.  This has been much discussed, and there are ways to correct for it, but this is a very technical issue. If you want to learn more, you might begin with .  Begin with this Wikipedia article, and go from there.

 In both cases, however, many phylogenetic analyses have confirmed the ancient position, and length of these two branches, so that is not a question  here..

Such long branches can lead to errors of interpretation at another level, however. A common misconception is that what we see in the current species, which occupy the very tips of these ancient lineages, will be similar to the  ancestors from which the lineage began, i.e. that these are archaic or primitive species.

But think about it.  These lineages have been around for more than 100 million years  (140 million for Amborella, 120 million  for Acorus).  Isn't it likely that the occupants of these lineages have changed somewhat over all those years?

Amborella fruits are single-seeded drupes, adapted for
dispersal by fruit-eating birds.  This is a specialization
that has evolved many times among angiosperms, including
most famously, cherries. Early angiosperms most
likely had fruits that split open to release several to many
seeds (see Were the first carpels plicate or ascidiate?
Small, unisexual flowers in dense clusters
 is also a specialization. Photo courtesy Joel McNeal.
Modern phylogenetic analyses are based primarily on molecular (DNA) comparisons, so in-and-of themselves tell us nothing about changes in the characteristics of the plants occupying the lineages.  So there is no direct basis for inferring what the first species in a lineage looked like or in  what ways their modern descendants may have changed.

As I argued in the previous posts, both Acorus and Amborella, as they exist today, exhibit a mix of ancient and specialized characteristics. They are both well-adapted to their environments, and have some distinctive specialized characteristics, particularly in their adaptations for pollination and seed dispersal. The Acorus and Amborella lineages have been around for such a long time, that it is rather absurd to think that they have not changed at all during that time. For groups that have good fossil records, we can trace such changes.  Fossils, for example, tell us that we modern humans have changed a great deal from the first members of our genus, even more from the ancestral genus Australopithecus!

The spadix-like inflorescence of Acorus led early
taxonomists to classify this genus with the Aroids.
Since the two families are not closely related, it is likely 
that the similarity is due to convergent evolution, driven by
adaptations for pollination. A spadix is a highly specialized
 way to arrange flowers and has evolved independently in a
number of families, including the Aroid, Palm, and 
Cyclanthus families. It is likely that the early monocots had
looser arrangements of flowers, more like those in most
Alismatales, and that dense flower spikes were not
characteristic of the first members of the lineage.
The folded and fused (equitant) leaves of Acorus, are
also a specialized adaptation that has occurred in many
unrelated families, most famously in several members
of the Iris Family.
How do we know, or at least develop hypotheses, as to what changes have taken place in a lineage in the absence of any fossils?  We can look at the characteristics of other early branches to see what they have in common, and hypothesize that the shared characteristics were present in their common ancestor.

 We can also analyze how particular characteristics might have arisen as adaptations to natural selective pressures, and determine which are most likely ancestral, and which are more specialized. Adaptations arise in logical sequences and often become canalized in non-reversible directions (see What is an adaptation? and G. L. Stebbins and the process of adaptive modification)

Both in comparison with other related groups, and in considering likely sequences of adaptations, Amborella and Acorus are specialized in some ways. For Amborella, small, numerous, unisexual flowers in clusters, and red, single-seeded fruits are both features that are more specialized than in other archaic angiosperms. For Acorus, the dense spikes of flowers with fused carpels (see also Were the first moncots syncarpous?) and the the leaves with the two sides fused together (equitqnt are specialized features, that have evolved independently in a number of families from more generalized types.

Wednesday, September 18, 2019

Guide to the mosses of central Florida

I have spent much time in the past few years studying the mosses of central Florida and posting portraits of the common species.  This work has culminated in a Guide and Interactive key, which has now been posted as part of the Atlas of Florida Plants..You can find the link on the Atlas home page, in the right column.

The guide is in  pdf format, so no special software is needed to use the key.  Though it can be printed
Page 1 of the key, showing the three initial choices. Move
through the key by clicking on arrows. One can also go
directly to the index by clicking the box in the upper right.
out, it is designed to be used on-line, or off-line with computer or cell phone, as there are active links leading the user from one part of the guide to another.

The key leads to species profile pages, similar to the postings I have done on this blog site, but briefer.  Currently, the guide covers 59 common mosses of central Florida, but as stated in the introduction, it is a work in progress.  The index at the back of the guide includes all species reported as occurring in Florida, and as we are able to include additional species, the guide potentially will morph into one that covers the entire state.  The guide will therefore be periodically upgraded and reposted. Those of you who have been following the moss posts are encouraged to notify me of any errors you see in the key, any information or photos of additional species, or any other suggestions.

Thanks for your interest and support.
On the species profile pages, one can find photographs, maps of distribution, and a link to the species page in the Atlas (logo under the map).  One can also go to the  index to see what other species are reported from Florida, or return to the key.

Friday, April 19, 2019

Theme and Variation - the Amaryllidaceae

The primary types of cultivated amaryllis are in the genus Hippeastrum.  
Their flowers are mostly shades and mixes of red, pink, and white. 
This is  one of my favorite cultivars, "Eye-catcher."
This spring, while I was waiting eagerly for the amaryllis plants in my yard to bloom, I started reflecting on
the marvelous family to which they belong, and how nicely they represent a fascinating aspect of plant evolution.

The Amaryllis family is known and beloved worldwide, even by people unfamiliar with its technical name or taxonomy, for it provides us with a variety of unique spring-flowering bulbs and perennials, from daffodils to subtropical amaryllis and tropical Crinums.

As presently defined, Amaryllis (technically the genus Hippeastrum), daffodils (Narcissus) and Crinum all belong to the subfamily Amarylliodeae. Onion, garlic, etc.are also members of the family, constituting the subfamily Allioideae.   Finally, the blue-flowered "Lily-of-the-Nile" (Agapanthus), from southern Africa, is technically in it's own subfamily, Agapanthoideae.  Altogether, there are some 1600 species in 75 genera, found naturally on every unfrozen continent.
Daffodils are specialized members of  the genus Narcissus, in which the umbel has been reduced to a single flower.

The subfamily Agapanthoideae consists of the single genus Agapanthus from
southern Africa. Flowers are blue to white.

The onion subfamily,  Allioideae, contains numerous aromatic and edible species.
The characteristic pungent fragrances are based on allyl sulfides,
which in nature  act as deterrents to insect pests.

The true bulbs of onions and amaryllis are made up of
the swollen bases of recent leaves that encircle the
central stem.  The outermost layers, representing
 older leaf bases, become dried and paper-like,
 which protects the fresh inner layers from drying out.
 This gives rise to the designation "tunicate bulbs,"
differing from the scale-bulbs of the true lilies.
Photo by Amada44, CC BY-SA 3.0.

So what defines this family? What is the common theme upon which the 1600 species are variants? The vast majority of the species in this family are geophytes, plants that survive adverse seasons underground. Most species form bulbs, but some, like Agapanthus and certain members of the Allioideae, employ underground rhizomes instead.  The leaves are strap-shaped (sometimes tubular and hollow in the onions) and extend themselves upward from the bulb by basal intercalary meristems (see "How the grass leaf got its stripes").  This is the most common form of leaf in the monocots, and it varies little in this family.

True, or tunicate bulbs (see illustration to the left), differing from the scale-bulbs of the true lilies, do seem to be a unique invention of this family,  though some members of the Lily family, such as tulips, have evolved a similar type of bulb independently.

Flowers in the Amaryllidaceae  undergo preliminary 
development below ground, between leaves or within the 
bulb and are protected by a closed sheath.  The enclosed 
bud is then pushed upward by the intercalary growth of  
the stalk.

But it is how the flowers emerge from the bulbs that is the most iconic, revolutionary, and consistent theme of the family.  Flowers form below ground, tightly enveloped in a protective sheath.   Below each inflorescence bud, a stalk (the peduncle) develops and lengthens through basal intercalary growth (i.e. new tissues are produced at the base of the stalk, pushing older tissues and the inflorescence bud upwards).  After rising to optimum height for pollination and eventual seed dispersal, the sheath splits open to reveal a simple umbel, i.e. one to many flowers arising from a single point at the tip of the stalk, roughly forming the shape of an umbrella or sometimes an entire sphere.

This proved to be a remarkably effective way to protect and elevate the flowers, for after it evolved in the common ancestors of the family, descendant species spread worldwide, adapting to different climates, soils, and pollinators. Such a spreading diversification is called an adaptive radiation. Note that the special structure and growth form of the inflorescence remained essentially unchanged throughout the family, while details of flower structure and color, fruit type, and physiological adaptations diversified.

Yellow flowers are uncommon in the Amaryllidaceae, but found here in
Lycoris aureus.  Photo by Tomago Moffle, CC BY-SA 3.0.
 The importance of this discussion is not simply to say how wonderful and unique the Amaryllidaceae is, but to stimulate us, particularly those of us who are teachers, to look for similar patterns of breakthrough adaptations followed by adaptive radiation throughout the plant kingdom.

Almost any genus, and sometimes a whole family can be seen to be based on some "great idea," i.e. some new structure, growth pattern, flower type, etc., that gave the ancestral species an advantage and allowed its descendants to diversify into great numbers.  Two simple examples are the genus Aquilegia (columbines) with its nectar spurs arising from each of the five petals, and the genus Euphorbia, with its highly compact flowering units called cyathia.

How many examples can you find? Can you explain the adaptive value of the distinctive features?
Each yellowish, red-tipped structure in this Poinsettia
(genus Euphorbia) is a cyathium, a cupule containing several
tiny flowers.

The highly distinctive flowers of Aquilegia feature a nectar
spur projecting backwards from each petal.

The giant crinum, C. asiaticum, from southern China, is an tropical evergreen
plant that develops a pseudostem, similar to that of the banana, made of the
tubular bases of the leaves.

Wednesday, March 27, 2019

Mosses of Central Florida 52. Gemmabryum apiculatum

Gemmabrum apiculatum forms thick cushions, with well-spaced leaves on
the shoots.
Gemmabryum apiculatum (Schwagrichen) J. R. Spence & H. P. Ramsay (Bryaceae) forms colonies of tiny, upright leafy shoots on damp soil in shady areas.  Leaves are long-ovate, well-spaced along the stems, and mostly 1 mm or more in length. Leaf cells are narrower than in related species, 6 to 8 times longer than wide, and become square toward the base.

The species characteristically forms tiny reproductive tubers or bulbils along the rhizoids in the soil or in the axils of the leaves. Bulbils are brown, pear-shaped, and 40-80 ┬Ám long. I have not yet seen spore capsules in our area.

Brown, pear-shaped bulbils in the leaf axils are characteristic of
Gemmabryum apiculatum. Photo by Ainun Nadhifah
Gemmabryum apiculatum is probably to be found throughout the state, as it is found  in coastal regions of other southeastern states, though our documented specimens are from central Florida southward. It is also found widely in the tropics. 
G. coronatum has a similar distribution, with some reports from the north.  The leaves tend to be rolled at the margins, and the leave cells are shorter, 3-4 times as long as wide.
A third species, G. exile, has been reported only from Collier County, but is easily recognized by its stringy stems and small, folded leaves.

The leaf of Gemmabryum apiculatum features a strong
 midrib, and elongate cells that become squarish toward the base,
Photo by Ainun Nadhifah