Category Archives: Plants

Roger Williams Park Botanical Center

On Saturday my family and I visited the Botanical Center at Providence’s Roger Williams Park.  Here are some of the more interesting plants we saw:

To begin, here’s the fluffy flower of Calliandra haematocephala, also called the powderpuff tree or stickpea:


Next up: the elephant cactus, Pachycereus pringlei, can apparently reach almost 20 meters tall! The Roger Williams Park cactus is so tall its top is tied to a ceiling rafter, but I was still more impressed by its spines:


Cactus spines deserve their own post someday, but until that day here’s some fun reading on what spines are, exactly.

Aha! Here we have some species of sundew (Drosera) cohabiting a lovely little bog with some species of bladderwort (Utricularia — perhaps U. livida)!  Sundews capture insects and other small prey that lands on their many sticky tentacles. Utricularia, you might recall, suck small animals into bladders and eat them.  Both are tremendously impressive:


For good measure, here’s a carnivorous pitcher plant too — I believe it’s a species of Sarracenia.


Now here’s something new — a Begonia rex of the “Escargot” variety.  I don’t believe I’ve ever seen a leaf take this form before.  It looks like it crawled out of the sea:


Before finishing up, let’s take a moment to marvel.  Cactus spines are likely modified leaves.  Sundews, bladderworts, and pitcher plants all developed traps — some active, some passive, all capable of capturing and digesting prey — that are highly modified leaves.  And the above Begonia rex “Escargot” sports leaf modifications of a different sort.  Perhaps that spiral shape is practical in some way I haven’t thought of, but regardless of utility it is quite beautiful.  All these structures are leaves, and wow! how different they are.

I started with a flower and I’ll end with a flower. This hibiscus stood out to me mainly because it made such a contrast to the cold, snowy outside visible through the greenhouse panes behind it.


Ah, the promise of summer.

Utricularia Suck Small Animals Into Bladders And Eat Them

On December 2, 1874, the remarkable Mary Treat wrote to Charles Darwin:

I have been studying the bladder-bearing species of Utricularia off and on the last year, and am now fully satisfied that they are the most wonderful carnivorous plants that I have yet seen. The so-called little bladders seem to be receptacles for digesting animal food. Not only small animalcules are lured into these receptacles, but animals large enough to be distinctly seen with the naked eye; and by holding the little bladders up to the light the movements of the animals can be seen with the unassisted eye.

We’ll get to Darwin’s response in a bit, but for now let’s ask: just what are these wonderful bladder-bearing botanical beasts to which Treat was referring?

Utricularia is a genus comprising several species of carnivorous plants called bladderworts.  Most (but not all) of these are aquatic and capture their prey by the use of so-called bladder traps or “utricles.”

Utricularia traps, courtesy of Michal Rubeš via wikimedia commons.

According to a review article by Elzbieta Krol and colleagues, Utricularia‘s “[s]uction-traps (bladders) are ranked among the most complex leaf structures ever to have been examined in plants.”  The traps work like this: A plant’s bladder forces water out, creating a sort of vacuum within the bladder and stored energy potential in the bladder walls.  At one end of the bladder is a tightly sealed valve rimmed by several hairs.  These hairs act as triggers for the bladder trap.  According to Krol, “each trigger hair acts as a lever, breaking the seal and releasing the energy whenever something (living creature or strong current) disturbs it.”  In other words, a light tap on one of these hairs causes the bladder to suck whatever happens to be outside the valve into the bladder.  Inside, the captured prey becomes plant food.

These bladders are quite impressive when you consider what they can trap, as listed by Krol (referencing Darwin): “aquatic species [of Utricularia] can hold … substantial prey, such as crustacean zooplankton (e.g. water fleas), nematodes, mosquito larvae, insects, tadpoles and even small fish.”  Apparently, Krol notes, they also end up eating a lot of algae.

An aquatic plant with complex bladder traps that allow it to eat fish?  Mary Treat called it wonderful, Elzbieta Krol calls it “truly outstanding,” and I say it’s tremendously impressive.

And speaking again of Mary Treat, what of her correspondence with Charles Darwin?

In the months following Treat’s letter to Darwin, he published his book Insectivorous Plants and she published an article in Harpers Magazine titled “Is the valve of Utricularia sensitive?”  Darwin had apparently suggested in his book that Utricularia were passive feeders, while Treat very respectfully disagreed:

Mr. Darwin says the valve does not appear to be in the least irritable, and continues (Insectivorous Plants, page 408): “We may therefore conclude that the animals enter merely by forcing their way through the slit-like orifice, their heads serving as a wedge.” But we have seen in the instances of the mosquito and chironomus larvae [each of which was trapped tail-first] that this is not the case; the head does not serve as a wedge. But what is the force that impels them into the utricle? It seems too bad to try to overthrow a plausible theory and offer nothing better in its stead. But what can I do? The play is enacted before me, and I have tried in vain to get behind the scenes to learn what the power is that impels the larva into the utricle. No doubt if Mr. Darwin had had the excellent material that I had to work with, with his keener insight he would have ferreted out the cause.

If within the utricle was a partial vacuum, the sudden opening of the valve would create sufficient force to carry whatever happened to be in close proximity into the utricle; and this illustrates the movement we see executed. But how could a vacuum be formed?

Treat attempted to send Darwin some Utricularia specimens and her article; Darwin at first received the former but not the latter.  He responded colorfully:

The specimens which you have sent of Utricularia are most beautiful & excellently preserved. I shall feel great interest in reading your account of them when published.

I am sorry to say that I never received the article in Harpers on the sensitivity of the valve in Utricularia,— a subject which drives me half mad.— If you have been able to prove either side of the case, I beg you tell me exact title & date of the number, which I can then easily pursue.

About a month later, after another letter from Treat, Darwin read the article and wrote to her:

My dear Madam

I have received your kind letter & the article which I have read with the greatest interest. It certainly appears from your excellent observations that the valve was sensitive … but I cannot understand why I could never with all my pains excite any movement. It is pretty clear I am quite wrong about the head acting like a wedge.— The indraught of the living larvæ is astonishing. …

I am not well & am staying away from my home for rest, so pray excuse brevity. Wishing you success of every kind in your admirable work

I remain | Dear Madam | Yours very faithfully | Ch. Darwin

So there you have it.

P.S.  In the course of researching this post, I learned that there are native Utricularia — as well as Drosera (sundews) and Sarracenia (pitcher plants) — residing in Rhode Island’s wetlands.  I am excited to have new things to look for when tromping around outside this summer!


Krol, E.; Plancho, B.J.; Adamec, L.; Stolarz, M.; Dziubinska, H.; Trebacz, K.  2011.  Quite a few reasons for calling carnivores ‘the most wonderful plants in the world. Annals of Botany 109 (1): 47–64.doi:10.1093/aob/mcr249

Wigeongrass is Unexpectedly Cool

In my professional life I work on addressing stormwater pollution (among other things). Recently this got me thinking: what all was in the bay water I used to swim in?

Wigeongrass may appear unassuming, but don’t be fooled!  It’ll send pollinated bubbles after you.  Image courtesy of stonebird via flickr.

As a child I swam in Langford Creek, a broad and slow water body that flows into the Chester River and from there to the Chesapeake Bay.  Back then, I enjoyed seeing ospreys overhead, and I loved swimming under docks to check out barnacle colonies and birds’ nests.  And love doesn’t even quite capture the feeling of peeing off a boat at night to see the water respond by glowing green (perhaps a topic for another post?).  But I didn’t think much about the question of water quality, despite being vaguely aware that runoff from chicken farms was reaching the Chesapeake, and that the Chester River was directly between some of the farms and the Bay.

Now that I am accustomed to thinking about water quality, I figured I could likely pick out some interesting fecal coliform bacterium I shared the water with once upon a time.  Or maybe an obnoxious alga.  Instead, I found something more pleasant: wigeongrass.

A 1997 survey of submerged aquatic vegetation in the Chesapeake Bay [pdf] reported the following underwater plants in Langford Creek: “R. maritima, M. spicatum, E. canadensis, P. perfoliatus, and Z. palustris.”  I liked what I saw from R. maritima and looked no further.

R. maritima is more lengthily known as Ruppia maritima, or colloquially as wigeongrass.  According to Harold Kantrud, writing back in 1991 for the U.S. Fish and Wildlife ServiceR. maritima received its name from Linnaeus in the mid 1700s.  And wigeongrass may be essential to ducks (which makes sense given that a wigeon is a kind of duck): Kantrud quotes a 1915 author writing “bays that have kept their wigeon-grass have kept their ducks; those in which the plant has been destroyed by influxes of mud and filling up of the inlets have lost them.”  So that in itself is moderately interesting.

What’s more interesting to me are a couple odd properties of R. maritima.

First, R. maritima devotes considerable energy to growing roots that it doesn’t seem to use.  The plant apparently grows fine when free-floating and draws in no nutrients through its roots; nevertheless, even “detached plant parts” will immediately send out roots.  Given this energy expenditure, Kantrud concludes that “roots probably serve some function.”  We just don’t seem to know what.  I tried to confirm this with a search of more recent scholarship on Google scholar and still came up empty.  But then again, I haven’t studied plants properly since high school biology about fifteen years ago, so this might just be my ignorance showing through.

Second, R. maritima can reproduce in three ways, one of which is unexpectedly cool.  Maybe you prefer methods one (asexual reproduction) or two (self-pollination), but my favorite method is number three: bubble-assisted.  The anther of R. maritima‘s flower — the part responsible for pollen release — “burst[s] and release[s] pollen, aided by gas bubbles that accumulate inside the anther sac.”  The pollen grains then ride the bubbles in search of other R. maritima specimens to cross-pollinate with.  Sounds like fun!

And bubble-riding pollen naturally leads to some good news: apparently R. maritima is a bedrock species of a healthy estuary.  Here’s a lightly edited summary of why R. maritima and other sea grasses matter, from the Narragansett Bay Estuary Program: “Seagrass beds provide shelter and feeding grounds for juvenile fish, crabs, shellfish, and birds, and act as a biological filters and erosion control by trapping sediments in interconnected root structures known as rhizomes.”  So the abundance of wigeongrass in Langford Creek in 1997 — a year I must have swum there — was a sign of good health.  Phew.

(Then again, I also used to fish in Langford Creek, and apparently PCBs have been discovered in fish there — eek.)

Delaware to Connecticut to Rhode Island: Tuliptree, Beech, Chestnut & Cattail

Walking in the woods in Delaware, my daughter found these …

tulip and beech

… and was curious.  What are they?

On the left is a seed cone of the tuliptree, Liriodendron tulipifera (you might also know it as tulip poplar).  Tuliptree cones are made up of a single point — like a knight’s lance — surrounded by many samaras (seed structures perhaps typified by maple “helicopters,” and a great word to know).  These seed cones enchanted me as a child, but I seldom find them here in Rhode Island.  It turns out that Liriodendrons just don’t live around here much — zoom in to the county level for Massachusetts and Rhode Island on this NRCS map, and you’ll see that they don’t seem to exist in southeastern New England’s coastal areas.  This is too bad.  With tuliptrees scarce in Rhode Island, here’s what we’re missing out on according to Donald Culross Peattie in A Natural History of North American Trees:

The flowers, which give it this name, are yellow or orange at base, a light greenish shade above. Almost as brilliant are the leaves when they first appear, a glossy, sunshiny pale green; they deepen in tint in summer and, in autumn, turn a rich, rejoicing gold.  Even in winter the tree is still not unadorned, for the axis of the cone remains, candelabrum fashion, erect on the bare twig when all the seeds have fallen.  No wonder that in the gardens of France and England this is one of the most popular of all American species.

Impressive indeed.

On the right is the shell of a nut from an American beech tree, Fagus grandifolia.  These shells were my bane when I was a child; a large beech tree would deposit these small, spiky monstrosities all over our backyard, significantly hampering barefoot play.  Now, though, I miss them — as it turns out, “Fagus grandifolia (American Beech) is uncommon along the coast of southern New England.”  Rhode Island’s climate and ecology so often feel like the Delaware woods where I grew up that these little differences always surprise me.

On our drive back from Delaware to Rhode Island at the end of the holiday weekend, we stopped by Connecticut’s New Canaan Nature Center. My daughter, while playing in the children’s garden, found lots of these …


… and was intrigued.  Talk about monstrosities!

The spiny husk was unfamiliar to me, but when I opened it up I recognized the chestnut inside.  It turns out that the American chestnut tree, Castanea dentata, was all but wiped out by blight in the early 20th century and has only gradually been returning to the east coast of the United States (with some help).

Interestingly, beeches and chestnuts are both members of the family Fagacea, which comes from the Greek for “to eat.”  Yes, friends, the contents of those spiky husks are very edible (no surprise with the chestnut, but perhaps for the beech).  Let’s check in again with Lee Peterson’s A Field Guide to Edible Wild Plants, where American beech and chestnut appear one after another on the same page:

The thin-shelled nuts [of American beech] have sweet kernels that are delicious roasted and eaten whole, or ground into flour. … Gather them after they drop from the trees during the first frosty nights in October.

Because of Chestnut blight, this species [American chestnut] now occurs mostly as sprouts from old stumps. … Nowadays few trees reach sufficient maturity to produce more than a few nuts.  If you do find enough to make collection worthwhile, gather the nuts after the first frost splits the husks open.  Once the husks and bitter pith are removed, the kernels are sweet and delicious.

Looks like we missed out on some good eating.

Finally, New Canaan Nature Center also features a “cattail marsh.”  In light of my previous hand-wringing over phragmites potentially poisoning cattails, it was nice to see some cattails thriving.



Peattie’s description of the American beech in A Natural History of North American Trees is too poetic not to include here, even though the nuts aren’t mentioned:

In very early spring, an unearthly pale pure green clothes the tree in a misty nimbus of light. As the foliage matures, it becomes a translucent blue green through which the light, but not the heat, of the summer day comes clearly. And in autumn these delicate leaves, borne chiefly on the ends of the branchlets and largely in one plane, in broad flat sprays, turn a soft clear yellow. Then is the Beech translated. As the sun of Indian summer bathes the great tree, it stands in a profound autumnal calm, enveloped in a golden light that hallows all about it.

Cattails Are Very Edible; Phragmites Want to Poison Them

Visiting family in Delaware, I rediscovered an old book called A Field Guide to Edible Wild Plants by Lee Peterson.  Figuring a post on an edible plant would be appropriate for Thanksgiving, I cracked the book and was captivated by this note on Typha latifolia, also known as the common cattail:

Probably no other plant, wild or domestic, is more versatile than Common Cattail.  In addition to yielding food year-round, it provides the material for making torches, mattresses, rush seats, and flower arrangements.

That’s the text accompanying the plate image of the plant.  The full text is full of more lush detail on just how one might eat cattails year-round.  The edible portions of cattails include “young shoots and stalks, immature flower spikes, pollen, sprouts, [and] rootstock.”  I think my favorite detail is this:

In earliest spring as they begin to extend, but before they break through the surface of the mud, these sprouts can be peeled, boiled briefly, and pickled in hot vinegar.  In addition, the starchy core at the base of each sprout can be prepared like a potato.

Who knew?

I thought I’d remembered that cattails were in danger of replacement by invasive Phragmites here on the east coast of the United States.  Phrases from the Wikipedia “cattail” entry like “dominant competitors” and “aggressive,” as well as tips for destroying cattails through burning and flooding made me doubt myself.

Other sources, though, bear out the narrative of Phragmites displacing cattails.  So this led to new questions — most centrally, if cattails are so “dominant” and “aggressive,” then how are they being displaced by Phragmites?

It turns out the likely answer to this question emerges from Delaware too: researchers at the University of Delaware discovered a few years ago that upon exposure to UV irradiation, a root-secreted toxin from Phragmites facilitates rhizotoxicity in susceptible plant species.”  In other words, sunlight leads Phragmites to release poison from their roots that kills competitors.  This result led the researchers to “hypothesize that the photo-chemically transformed products of GA in aquatic ecosystems could be potentially toxic to competing grass species leading to marsh invasion and monoculture formation by Phragmites.”

I’ll be honest: it’s Thanksgiving, so I’m not going to put the time into figuring out the mechanism for this competitor-poisoning behavior by Phragmites right now.  It does sound really interesting, though, so look for it here later.  For now, let’s just take a moment to thank members of the genus Typha for being so useful — and apparently delicious — and to stand in awe of the complexity of plant life that surrounds us every day.

A Thousand-year-old, Exoskeleton-building Arctic Alga

The exoskeleton of a thousand-year-old Arctic alga has allowed scientists to reconstruct historical data on Arctic temperatures and sea-ice cover.  Not surprisingly, according to the  abstract of a new paper from University of Toronto professor Jochen Halfar, “algae show that … the 20th century exhibited the lowest sea-ice cover in the past 646 years.”

Perhaps more suprising than the recent drastic loss of Arctic sea ice is the fact that there exists a thousand-year-old, exoskeleton-building, Arctic-dwelling alga in the first place.  It’s called Clathromorphum compactum.  And it’s pink.  Let’s take a closer look and see how C. compactum has allowed scientists to study ancient sea ice.

A master’s thesis from a former student of Prof. Halfar’s [pdf] provides some details about Clathromorphum compactum and its exoskeleton-building ability:

C. compactum has been found in marine habitats of the Northern Hemisphere, including the North Atlantic, North Pacific, and the Arctic oceans. This long-lived crustose coralline alga builds its skeleton by depositing annual layers of high-magnesium calcite.

Morphologically C. compactum displays cell differentiation with small and heavily calcified cells formed during the cold months, separated by large and poorly calcified cells built during the warm periods. This abrupt change is marked by a growth line.

In other words, take a cross-section of one of these skeletons and you’ll see rings just like the ones that provide evidence of a tree’s age and health record.

The same master’s thesis explains a little bit about how C. compactum and its relatives build their skeletons:

Crustose coralline algae build their calcified skeletons by precipitating calcite crystals directly in the vegetative cell-wall.  While the external factors influencing crustose coralline algae calcification such as temperature, salinity, pH, light, and food availability have been investigated, the physiological processes are less understood.

The effects of temperature and light on algal skeleton-building are particularly significant to anyone who wants to extract information from the skeletons’ growth lines.

As to temperature, the warmer the weather, the more magnesium the algae’s skeletons contain.  This means that the amount of magnesium in a particular ring of a skeleton’s cross-section can show us how warm or cold the water was when the skeleton was built.

And as to light, sea ice blocks light and inhibits the alga from growing at all.

The takeaway is this: when there’s warm water and not much sea ice, C. compactum builds thick, magnesium rich layers of exoskeleton.  And according to Prof. Halfar’s abstract, that’s what’s been happening for the last hundred-plus years:

The 646-y multisite record from the Canadian Arctic indicates that during the Little Ice Age, sea ice was extensive but highly variable on subdecadal time scales and coincided with an expansion of ice-dependent Thule/Labrador Inuit sea mammal hunters in the region. The past 150 y instead have been characterized by sea ice exhibiting multidecadal variability with a long-term decline distinctly steeper than at any time since the 14th century.

So please take a moment to thank C. compactum and its peculiarities for serving science and confirming that we’re busily destroying our planet.

P.S. Apparently, while the alga Heterosigma akashiwo is not a plant, the alga Clathromorphum compactum is a plant — a plant that builds exoskeletons.  Weird.

A 20th Century Extinction: Thismia americana, fungus-feeding plant

I made a bet with myself that I could find an interesting North American plant species that went extinct in the last 100 years.  It took only about 5 minutes to win the bet.

In 1913, botanist Norma Pfeiffer earned her PhD from the University of Chicago at age 24. 

There’s so much impressive material in that last sentence that I’d recommend you read it again. 

Ok, now we can continue.  Dr. Pfeiffer would go on to become an expert on lilies (so says the New York Times), but it’s her PhD work that’s relevant here.  As part of her thesis, Dr. Pfeiffer discovered the species Thismia americana right in Chicago.

Why was — and is — T. americana noteworthy?  We’ll let Dr. Pfeiffer explain first in her 1914 paper “Morphology of Thismia americana“:

The entire plant is glabrous and white, save in the 6 divisions of the perianth, where free, and in the disk closing the perianth mouth.  Here there is a delicate blue-green color, deeper in the raised ring about the aperture of the disk. …

In the older part of a root of Thismia, there is evident a very conspicuous epidermis. … The layer of cells immediately below the epidermis is packed with the thick-walled, branching mycelium of a coarse fungus. …

Since the fungi occur in the root, the absorptive region, and not in the stem, they would seem to have some connection with water and food supply.

Hm.  A 2004 story in the publication Chicago Wilderness uses lay language:

Thismia americana was a mystery right from its discovery. Instead of drawing energy from the sun, Thismia fed on fungi that grew in its roots, spending much of the year underground. In midsummer, a tiny tube-like flower pushed upward an inch or so, and only the upper quarter actually emerged from the soil. Its three petals remained linked at the top of the tube, leaving arch-like entries for small insects to pollinate. Lacking chlorophyll, the entire plant was smooth and translucent white, with hints of pale blue-green stripes that deepened at the tip of the flower. By September, the blossoms seeded and withered, and the plant disappeared underground for another year.

Or, if you prefer, here’s the Chicago Tribune in 1991:

What makes the plant so unusual is that by all rights it should never have grown here. Its nearest relative is a tropical plant that is found in New Zealand, Australia and Tasmania. It contains no chlorophyll, the substance that allows other plants to make their own food and gives them their green color. Instead, thismia lives on soil nutrients that a fungus in its roots digests for it.

A plant that mostly lived underground, lacked chlorophyll, and instead of producing its own food ate only courtesy of root fungi?  Pretty neat.

Thismia Americana “was seen for five consecutive years, and it has never been found again despite repeated searches by scientists and botanical groups” [pdf]; accordingly, it is now generally believed to be extinct.