Mosses of Central Florida 8. Entodon seductrix

The small ovate leaves of Entodon seductrix are
pressed against the stem when dry, giving the stems
a rope-like appearance.  The sporangia are upright
and cylindrical, with two rows of teeth around the
mouth.

[For other mosses in this series, see the Table of Contents]

Entodon seductrix (Hedw.) Müll. Hal. (Entodontaceae) is a common, straggling moss with horizontal stems covered with short leaves, and with sporophytes arising along the sides.  This species is found throughout eastern North America, as far north as Ontario, and extending westward from Florida to Texas.  Our collections are from the middle of the state northward, so it's not clear how far south it extends.  It characteristically forms lush mats at the bases of trees.

This species is easily confused with Isopterygium tenerum. Like that species, leaf cells are elongate and slightly curved, and there is no midrib (costa).   The short leaves of E. seductrix, however, press closely to the stem when dry, while those of Isopterygium are spread out.  The two species differ most obviously when sporangia are present.  In E. seductrix they are upright, nearly symmetrical, and cylindrical, in contrast with the strongly curved sporangia Isopterygium.

Another species of Entodon in our state is E. macropodus, which has slightly larger leaves that remain spread out when dry, but the sporangia are still upright and cylindrical. This species is more southern in its distribution, occurring northward to Virginia and southward into tropical America.  It is also found in Japan.

The slender leaf cells of Entodon are like tiny worms, with
thick, clear walls between them. Toward the base, they
become more rectangular, but not conspicuously
inflated.

Were the first monocots syncarpous?

In my recent post on Acorus, I suggested that one of the ways this genus is specialized is that the three carpels within each flower are joined together into a single pistil (syncarpous).  Acorus is at the end of the earliest branch of the monocot tree -  the sister clade to all other monocots. Its various characteristics are therefore of great interest when discussing the nature of the first monocots.  Carpels are mostly free of one another (apocarpous) in many members of the Alismatales, the next most ancient branch of the monocot tree after Acorus.  Because carpels are also free in the archaic angiosperms of the ANITA grade, many magnolids, and some basal Eudicots, it seems most logical that the common ancestor of Acorus and the rest of the monocots also had free carpels.  That logical assumption, however, has recently been challenged by Sokoloff et al. (2013).

Carpels in ancient angiosperms were separate structures, each of which had to receive pollen individually from a visiting insect. Butomus, on the left, is a monocot in the Alismatales that retains separate carpels.  In more advanced angiosperms, such as the tulip on the right, also a monocot, carpels are fused together, with a common stigmatic area where a single deposit of pollen can fertilize all the ovules in the ovary.  Left photo by Sten Porse, right photo by Bernd Haynold,  both posted on Wikimedia Commons

Tradition and conventional wisdom hold that the fusion of carpels has adaptive value and is a more-or-less irreversible process. This was confirmed by Armbruster et al. (2002), who explored the advantages of shifting from apocarpy to syncarpy and estimated 17-26 separate instances of this shift among angiosperms. The fusion of carpels brings stigmas together in such a way that pollen is deposited in a single central location by a visiting insect.  Pollen tubes can then pass through the common style and enter into any of the carpel chambers, which is said to increase competition among pollen tubes, but also insures more even fertilization among the ovules in the ovary as a whole. Carpel fusion also reduces material needs as only the outer walls need to be fortified for protection of the developing ovules. Monocots were not analyzed in the Armbruster study, but apparently were assumed to be fundamentally syncarpous. 

The general trend among seed plants is for gradually tighter and deeper enclosure of ovules within protective stuructures,including the tighter closure and fusion of carpels.  Because of the adaptive advantage attached to this trend, reversals back to apocarpy are considered unlikely:

ovules on open, leaf-like structures (ancient seed ferns)----->
     ovules on specialized leaf-like, cone-like, or shoot-like structures (gymnosperms) ------>
          ovules within loosely-closed, leaf-like carpels (stem angiosperms) ------->
                carpels apocarpous (early crown-group angiosperms and basal magnolids, eudicots, and monocots)                                   ------->
                     carpels syncarpous or unicarpellate, and sometimes surrounded by tissues of the receptacle                                                               ("inferior ovary") (most advanced angiosperms)

Armbruster and colleagues did detect two probable reversals from syncarpy to apocarpy among  eudicots (in the genus Crossosoma and members of the Saxifragales), and speculated that the advantage might be to extend the period of ovule fertilization so as to receive pollen from different sources. It's not clear that such an extension happens in these examples, however, as each only has a few carpels.  Likewise, in archaic monocots like Butomus (in the Alismatales), the small number of carpels are receptive at the same time and for only one day (Bhardwaj & Eckert 2001).   In Sagittaria, also in the Alismatales, the carpels are more numerous and physically spread out, but again are receptive at the same time for only one day.  If multiple visitors fail to arrive during that window, it potentially leaves carpels unfertilized. Multiple insect visitors are possible in one day, but does the potential advantage of genetically different pollen arriving in the same flower outweigh the usual advantages of syncarpy? The idea needs fleshing out with stronger selective arguments and actual examples of it working.   

From another perspective, if there is an advantage in spreading out the fertilization of ovules in either time or space, a much simpler way to effect that advantage in syncarpous flowers is to make the flowers smaller, with just one or a few ovules in each, and produce a series of them.  This has in fact happened many times, as in the Saururaceae, Piperaceae, Asteraceae, palms, aroids, etc. I am not aware of any series of carpels in an apocarpous flower functioning this way, let alone a syncarpous ovary splitting apart to do so.

 Despite the foregoing, Sokoloff et al. (2013) concluded that the earliest monocots were syncarpous and that apocarpous flowers evolved several times among them.  In some cases, according to this scenario, syncarpy re-evolved a short time later from newly-apocarpous ancestors. What is the basis for this counter-intuitive proposal?  It appears not to be based simply on the fact that the most ancient monocot lineage (Acorus) is syncarpous, but on a more extensive theoretical exercise involving cladistic analysis plus an additional step of "optimized parsimony analysis."

DNA-based cladistic analysis provides a clear, and increasingly accurate picture of the ancestral branching patterns of groups of organisms - - i.e. a phylogenetic tree.  When only DNA information is used, the tree tells us nothing about when and where new adaptive traits arose.  For this, we can "map" such physical characteristics onto the tree. For example, we can make a little mark on each branch containing only species known to be syncarpous.  If two adjacent (sister) branches have syncarpous flowers, we assume their common ancestor had the same.  It is also possible, however, that syncarpy evolved  independently on each branch from an ancestor that was apocarpous.  But this interpretation is less parsimonius, because it involves more independent evolutionary changes (syncarpy evolved twice instead of only once).  

Optimized parsimony  analysis takes into consideration a wide variety of tests, assumptions, taxa lists, character definitions, etc. for the same set of data and determines the most parsimonious interpretation of the evolution of particular characteristics.  Some of the tests  performed by Sokoloff et al. were ambiguous about the nature of the ancestors, but overall they suggested that syncarpous flowers were present first in the monocots.  Quite possibly, the basal position of syncarpous Acorus tilted the final results in this favor, raising again the questions I raised in my previous post.

So from this cladistic perspective, multiple evolution of apocarpous flowers from a syncarpous ancestor is more parsimonious than multiple origins of syncarpy from an apocarpous ancestor.  But does evolution necessarily follow the most parsimonious path?  In the real world, perhaps one evolutionary trend, because of its adaptive value, is more likely to occur multiple times than the opposite.  So to evaluate this proposal further, we need to consider the adaptive basis for each trend.   Sokoloff and colleagues in fact raised the question: “Assessing the functional and adaptive significance of evolutionary transformations is clearly important" ( p. 75). They proceed to reiterate the advantages of syncarpy, but made no suggestions as to why reversals might occur. They made another disturbing statement:  "Interestingly, in the monocot order Alismatales, congenital intercarpellary fusion was first lost and then re-appeared in three independent clades according to this scenario" (p. 64). One of those reversals would include the Butomus pictured above.

I recently outlined the principles advocated by Stebbins for evaluating alternate evolutionary scenarios (G. L.Stebbins and the process of adaptive modification).  These principles result in the "other parsimony," the parsimony in which sequences of adaptive changes are assumed to proceed along the simplest paths, or "along the lines of least resistance."  My example above, in which shifting to a series of small flowers, instead of splitting the ovary to make a series of separate carpels, is an example of such a simpler path.  Further, once a developmentally complex and highly functional structure like syncarpy evolves, one would need a rather powerful selective pressure to undo it, something giving an advantage to apocarpy strong enough to cancel out the documented benefits of  the syncarpous ovary.   No one has yet offered such an adaptive scenario.

Therefore, "cladistic parsimony" must be balanced against "adaptive parsimony."  Seventeen independent transformations from apocarpy to syncarpy may be more reasonable in view of selective pressures we know about than even one reversal.  I think it is therefore premature to dismiss apocarpy in the ancestral monocots.  Despite the fused carpels and other specializations of Acorus, apocarpy and looser forms of syncarpy (due to post-genital fusion) are widespread among the Alismatales, which are nearly as old as Acorus, and possibly more conservative with respect to the condition of their carpels.  In the palms as well, separate carpels occur in more archaic groups (Nypa and the Coryphoideae), though the first branch, the lepidocaryoid palms, are syncarpous. This is a more complex situation, however, as the palms appear to have originated among clades that were already syncarpous.  Still a scenario is needed for why fused carpels might become separate again in these palms.  Does such a scenario make sense in the real world of adaptive pressures?

References:

Armbruster, W. S.  , E. M. Debevec & M. F. Willson. 2002. Evolution of syncarpy in angiosperms: theoretical and phylogenetic analyses of the effects of carpel fusion on offspring quantity and quality. Journal of Evolutionary Biology 15 (4): 657-672.

Bhardwaj, M., Eckert, C. G. 2001. Functional analysis of synchronous dichogamy in flowering rush, Butomus umbellatus (Butomaceae). Am. J. Bot. 88(12):2204-13.

Sokoloff, D. D., M. V. Remizowa and P. J. Rudall. 2013. Is syncarpy an ancestral condition in monocots and core eudicots? in Early Events in Monocot Evolution, Eds.  P. Wilkin & S. J. Mayo. Cambridge University Press.

Mosses of Central Florida 7. Thuidium delicatulum

The leafy stems of  Thuidium delicatulum branch into a fern-like pattern.

The leaves are boat-shaped and packed densely
along the stem.

[For other mosses in this series, see the Table of Contents]

Thuidium delicatulum (Hedw.) Schimp. (Thuidiaceae) is easy to recognize due to its strikingly fern-like appearance.  Its leafy structure of course is not a true compound frond as in actual ferns, but a finely branched stem system with tiny leaves.

The small leaves have a weakly-developed midrib (costa).

The leaves are roughened with tiny tooth-like papillae.

The leaves are small with a weakly-developed midrib, and roundish to oval cells that each have strongly developed papillae (small clear bumps).  Branched filaments, called paraphyllia, are also present among the leaves. Sporangia are uncommon, but described as "elongate, asymmetric, and inclined" (Reese, 1984, Mosses of the Gulf South).

Slender, sometimes
branched paraphyllia
are found among the leaves.

Thuidium delicatulum is distributed widely in northern and eastern North America, as well as South America. It extends westward from Florida into Texas.  Another species in Central Florida is T. allenii, which has a similar branching structure, but less regular and more straggly, not quite giving the appearance of a fern.  The papillae are also smaller.  T. minutulum is found further north, and also in Highlands County, and has mostly simple, unbranched stems, and short, unbranched paraphyllia.  T. pygmaeum is similar, and has been found only in Jackson County.

G. L. Stebbins and the process of adaptive modification

The convergence of modern phylogenetics, genetics and evolutionary development (EVO-DEVO) has allowed us to make better and better hypotheses about the evolutionary history of plants, for which the fossil record still leaves many gaps.  There is another dimension to this fascinating pursuit, an older one that isn't talked about as much: the analysis of adaptive or evolutionary trends.  This was the core logic of evolutionary biology through much of the twentieth century, before cladistic analysis came to dominate.  The publication of "Flowering Plants: Evolution above the Species Level" by G. L. Stebbins in 1974 represented the finest of this approach.  Far from being obsolete, the thought processes of  Stebbins and other 20th century evolutionary biologists are still applicable to the various, sometimes controversial theories that are appearing currently.  In my opinion, Stebbins' book should be required reading for all graduate students of evolution.

Adaptive modification along the lines of least resistance

  One of the general principles of evolutionary biology is that evolutionary change, under the force of natural selection, will tend to proceed along the lines of least resistance - i.e. the simplest route. For example, a leafless cactus adapts to epiphytic life in the rain forest, not by reconstructing the leaves abandoned by its ancestors, but by flattening its stem segments into leaf-like units (e.g. genus Schlumbergia - the Christmas cactus).  This is one aspect of the bigger picture of evolutionary canalization, which essentially states that the possible adaptations of a plant species or individual organs are limited by what they already are.  A coconut has little prospect of evolving into an orchid-like capsule with millions of tiny, wind-pollinated seeds, just as an elephant has little prospect of evolving wings (or flying with its ears!).

Let me expand upon one of Stebbins' most lucid examples.  Suppose there is selective pressure for an increase in seed production.  This could occur for a variety of reasons: improved growing conditions, adaptation to a sunnier environment where smaller seeds can be created in greater numbers, and/or an increase in the numbers of seed-eating animals present.  All could all favor a species that increases its output.  How a species would respond to such a challenge would depend on its starting equipment.

A legume is a modified follicle containing a variable
number of seeds. Ovules are created in a
meristematic zone in the young carpel
 that can be increased or decreased. Photo by
by Renee Comet - NCI, posted on Wikipedia.

A species that has a fixed number of carpels in its flowers, but a variable number of ovules in each carpel, might respond by producing more ovules within each carpel.  The capsules of lilies, irises, and orchids, along with simpler follicles of columbines, delphiniums, etc. produce ovules in sequence from meristematic (embryonic) tissues within the carpel.  Simply continuing that activity for a longer period of time would result in more ovules.  To some extent, this flexibility is important on a day-to-day basis.  When conditions are poor, fewer ovules may be produced, and when better, more may be produced.  Extended onto an evolutionary scale, adaptations for more and more seed production can result.  Orchids represent one culmination of this trend, producing millions of tiny airborne seeds in each capsule. By the same token, reduction to a single seed is also possible from an ancestor in which the number is variable.

In the flower of a strawberry, the numerous carpels are
produced by the apical meristem in the embryonic bud.
Each will become a seed-like achene on the outside of
the swollen, Fruit-like receptacle (central stalk). Photo by
Papas2010, posted on Wikipedia.

In species that have a fixed number of ovules in each carpel, but a variable number of carpels in each flower, the number of carpels can be increased.  This is what happens in something like a strawberry (see "Why are the seeds of a strawberry on the outside?").   The tiny fruits of the strawberry (the seed-like structures on the outside of the swollen receptacle) are adapted as achenes. The number of seeds in each tiny carpel is rigidly fixed at one.  It would take an extraordinary amount of genetic and developmental reorganization to increase the number of seeds within each achene, which in the process would have to adapt to a different dispersal strategy.  The meristem in the center of the flower, which produces the carpels sequentially, however, can continue to operate a little longer and easily produce many more single-seeded carpels.
the number of carpels might be increased.

In a third "starting point," we have sunflowers and their relatives (family Asteraceae), in which flowers are highly canalized.  The actual flowers are tiny and crowded onto a dense head.  Each contains a single seed in a highly specialized ovary. It is inconceivable that a pressure for higher seed output would result in more seeds or more carpels being produced in each flower.  It is vastly simpler to increase the number of flowers within the composite head.  This is what we see in the massive cultivated sunflowers, which have evolved under human selection, compared with their wild relatives.

The massive sunflower is actually a composite head of several hundred tiny flowers that each bear a single seed.  The
size of the head depends on how long the central apical meristem actively produces new flowers (oldest flowers
around the outside are open, newer ones toward the inside are still in bud).  Photo by Amada44, posted in Wikipedia.

The imperative of evolutionary canalization, and modification along the lines of least resistance can be stronger than the imperative of parsimony in phylogenetic analysis.  It is the basis for my conclusion that the single-seeded drupes of Amborella represented a specialization from a more flexible common ancestor (see "What's so primitive about Amborella.")  I will also invoke these principles in some upcoming posts.

References cited

Stebbins, G. L. 1974.  Flowering Plants: Evolution above the Species Level.  Belknap Press of Harvard University.

What's so primitive about Amborella?

The male flowers of Amborella are crowded with stamens.
Photo by Scott Zona, posted on Wikipedia

The discovery that the lonely species Amborella trichopoda occupies the tip of the most ancient known clade of flowering plants has caused quite a sensation in the botanical community.  Here was the closest living relative of the common ancestor of all known flowering plants - a glimpse of what that ancestor might have been like! (Bailey & Swamy 1948).

Amborella is in the same position relative to angiosperms in genera, as Acorus is to other monocots.  I argued in a recent post (What's so primitive about Acorus?), however, that being at the tip of a very long evolutionary branch does not necessarily mean being exactly the same as the very first members of that branch.  It is likely in fact that some changes have been made as conditions and competition changed over the tens of millions of years since that ancient phylogenetic split.  I identified several ways in which Acorus was probably more advanced than some other archaic monocots that branched off slightly later.

The female flower of Amborella
contains several carpels and a few
sterile stamens.  The carpels are
ascidiate and unsealed. An opening
just below the stigma is blocked
only by a drop of fluid.
 Photo by Sangtae Kim

So we must consider that possibility with Amborella.  If Amborella is the sister group to all other known angiosperms, it must have split off somewhere between 120 and 140 million years ago, certainly time for a few changes to have occurred.  There may have been a whole family of amborellids early on, perhaps adapted for different light levels, soil types, pollinators, fruit dispersers, etc. Some may have even been flirting with the aquatic habitat, for the very next branch on the angiosperm tree consists of the waterlilies and their relatives.  We have no idea - because at present at least, we have no fossil record of this lineage.  All we have is the one species that survived to the present day.

To be sure, Amborella trichopoda,  has retained a number of truly archaic features. For one thing, it has the most primitive wood (consisting only of tracheids), of any living angiosperm (Carlquist & Schneider 2001). It also has very basic flowers, as we'll see below.

Amborella occurs in the rain forests of New Caledonian, a gentle environment isolated from both climate change and the hotbeds of aggressive evolution on the continents.  Other relics of past ages survive in similar habitats, including the nearly-as-ancient order Austrobaileyales.

If we include the Austrobaileyales and the Nymphaeales with Amborella in our analysis, we can create a more general picture of the ancestral angiosperm.  Together these three clades are referred to as the ANITA grade, and contrast with the higher angiosperms of the magnolids, eudiots, and monocots. Each can be assumed to have a different mix of ancestral and specialized characteristics.  The likely characteristics of the ancestral flower have been in fact derived from a study of this group (Endress 2001).

In this model, the ancestor of all known angiosperms had bisexual flowers consisting of simple, separate organs: tepals, stamens and carpels, which were spirally arranged and indefinite in number. Advancements from this model, such as carpels fused into a compound pistil, stamens in whorls of definite numbers, and tepals in two distinct whorls of sepals and petals, show up in various higher groups at different times.

Three other aspects of the carpels are also part of the model:

1. carpels are unsealed. They are open just below the stigmatic region, and entry of dirt, pathogens and small animals is blocked only by a drop of fluid. This contrasts with most modern carpels, which are completely  sealed by a tight suture.

2. carpels are ascidiate, i.e. urn-shaped. The wall of the carpel is smooth and seamless,  like a sock pulled up around its contents. This contrasts both with earlier accepted models of the first angiosperm carpels, and those of most modern angiosperms, which are plicate (folded).  In the plicate model, a row of ovules along each margin of an ancient, leaf-like structure were brought inside as the margins joined together in a tight suture.

3. carpels contain just a few ovules placed opposite the backbone of the carpel, though there is some variation. Amborella has just one ovule, some waterlilies have many.

The carpel of Amborella is ascidate and unsealed at the top,
though the stigma region shows a folded structure
consistent with the plicate model  of the carpel.
Drawing from Bailey & Swamy (1948)

In the plicate, or folded-leaf
model, the first carpels folded
or rolled together, bringing rows
of marginal ovules inside. The
two edges eventually became
tightly sealed by an interlocking
suture.
Drawing from the 1879
textbook by Asa Gray

Assuming that this correctly describes the flower of the common ancestor, Amborella is likely specialized in several ways.  First the flowers are relatively small compared to others like most waterlilies, Austrobaileya, and Illicium, and massed together in an apparent group display. Masses of small, whitish flowers are common among eudicots, magnolids and monocots. Examples include viburnum, most palms, and carrots/Queen Anne's lace. Such displays are adaptation for a particular pollination strategy involving a variety of insects and possibly wind (Thien, et al. 2003).

 The flowers are also unisexual, with pollen-producing flowers on separate plants from those that bear ovule-producing flowers.  Such an arrangement is likely  a means of avoiding self-pollination (Ferrandiz et al. 2010).  Similar patterns can be seen in a variety of other plants, such as date palms.  The fact that the female flowers contain  sterile stamens between the tepals and the carpels is compelling evidence that the ancestors of Amborella did indeed have bisexual flowers. This has recently been confirmed by Sauchet et al. (2017).

The fruits of Amborella are described as small drupes.  These are fleshy fruits with large seeds filled with food reserves, typically adapted for germination in shady forests.  Drupes are found among many different families of flowering plants, but to my knowledge are always the endpoints of evolution from more generalized ancestors with flexible ovule production.  In the Rose family, for example, drupes are found in the genus Prunus (plums, cherries, etc.), a specialized genus in a family that includes a wide variety of fruit types.

The bisexual flowers of Austrobaileya have a
number of carpels, each containing two rows of
 ovules, as well as flattened, blade-like stamens.
Source: http://www.naturalist.if.ua/?p=3585

Drupes are constrained developmentally to produce only one ovule, which becomes surrounded by a pit, a hard layer the develops from the inner fruit wall.  Reorganization of the development process to begin producing more ovules, and in two rows at that, would require numerous genetic changes.  It would conceivably happen if there were selective pressure to produce more, smaller seeds, but this could be  much more easily accomplished by increasing the number of carpels in the flower, or by increasing the number of flowers produced.  Such a rigidly one-seeded carpel is therefore not likely the ancestor of the variety of carpels and fruit types we find among angiosperms today, or even what we find in the ANITA grade. Something like the multi-seeded fruit of Austrobaileya is a much more likely starting point for all kinds of fruits, including drupes, berries, and capsules that open to release their seeds.

In sum, Amborella is likely specialized in its floral display, unisexual flowers, and single-seeded carpels.  In other ways, it does show its age: wood without vessels, simple, separate flower parts of indefinite numbers, and unsealed carpels.  Its present very limited distribution in forests of New Caledonia attest to its archaic status and its proximity to extinction.  The few ways in which it has specialized are probably the keys to it still being with us.

This discussion leads to a deeper question of the nature of the first angiosperm carpels, which evolved well before the common ancestor of living angiosperms.  Were they ascidiate or plicate? The ascidiate carpel itself may be an adaptation for making berries and drupes, maybe nuts and achenes as well, but does not lend itself to carpels that must reopen as capsules, follicles or legumes.  So were the very first carpels fleshy berries?  I'll take that up in a future post.

References:

Bailey I. W. and Swamy B. G. L. 1948 Amborella trichopoda Baill., a new morphological type of vesselless dicotyledon. Journal of the Arnold Arboretum 29: 245–254.

Carlquist, S. J. and E. L. Schneider. 2001. Amborella trichopoda: relationships with the Illiciales and implications for vessel origin. Pacific Science 55 (3): 305-312

Endress, P. K. 2001. The Flowers in Extant Basal Angiosperms and Inferences on Ancestral Flowers
International Journal of Plant Sciences 162 (5): 1111- 1140

Thien, L. B. , T. L. Sage, T. Jaffré, P. Bernhardt, V. Pontieri, P. H. Weston, D. Malloch, H. Azuma, S. W. Graham, M. A. McPherson, H. S. Rai, R. F. Sage and J-L. Dupre. 2003. The Population Structure and Floral Biology of Amborella trichopoda (Amborellaceae) Annals of the Missouri Botanical Garden 90 (3): 466-490.

Sauquet, Hervé, Balthazar, Maria von …Schönenberger,Jürg. 2017  The ancestral flower of angiosperms and its early diversification. Nature Communications volume 8, Article number: 16047  

Mosses of Central Florida 6. Ditrichum pallidum

Ditrichum pallidum plants are like tiny clumps
of grass.

[For other mosses in this series, see the Table of Contents]

Ditrichum pallidum (Hedw.) Hampe (Ditrichaceae) is one of the grass-like mosses. Each shoot consists of
a clump of elongate, grass-like leaves that consist mostly of an elongate midrib (costa). Cells in the upper section are elongate-rectangular, but overlapping and hard to distinguish.   The actual blade of the leaf flares out briefly at the base, where one can see relatively large ovate to rectangular cells.  The capsules rise from elongate, straight stalks, and  and remain more-or-less upright throughout.  At maturity, the capsules are narrow, nearly cylindrical, and with a single row of short teeth around the mouth, attached just below the surface.

Most of the leaf is the thick, prolonged tip of the
midrib, with elongate-rectangular cells.

Near the base, one can find the thin,
flaring blade, with ovate to
rectangular cells.

This species is widespread in both the old and new worlds, having been reported from Europe, Africa, Japan, and eastern North America.  It is common in Florida and found as far west as eastern Texas.  This distribution is consistent with its preference for disturbed soil along roads, fields, lawns, and forest openings.

When dry, the capsules are nearly cylindric, with
blunt tips. Just inside the mouth is a single row
of small teeth.

Medicinal plants in our own backyard

The discovery of plants with medicinal or health-promoting properties began with indigenous cultures around the world thousands of years ago.  The practice of herbal medicine is truly the "oldest profession," and even pre-dates humanity.  Chimpanzees are known to seek out certain plants in their native forests that can relieve illness or discomfort. One such plant comes from a shrub native to the forests of Africa called Aspilia (Asteraceae), which has been shown to kill bacteria, fungi and nematodes in the intestinal tract.  It may also serve as a stimulant - the morning coffee for chimps.  Each culture has discovered useful plants in their own backyards, and modern medicine is now slowly exploring that priceless knowledge and verifying what these people have known for a long time.

The prickly poppy, Argemone mexicana, was introduced into Africa in the
19th century and has been used as a medication against malaria almost
as long. Photo by B. Navez, posted in Wikipedia.

So it was a personal surprise to me - even though I teach a course in Medicinal Botany - that a plant frequently found in my own backyard has within it compounds that may cure malaria.  The plant is Argemone mexicana, the prickly poppy. The new information was featured in the recent issue (June 2014) of Scientific American, in the article "Seeds of a Cure," by Brendan Borrell.  The article describes the efforts by researchers working in the field in Africa, Mali to be specific, to document the effectiveness of the plant among people taking this natural medicine as an herbal tea.  The researchers documented a successful cure rate of about 89%, which compares quite favorably with the 95% rate of the much more expensive conventional treatments based on artemisin.

I went back to my classic textbook on medicinal botany by Lewis and Lewis, and found mention of prickly poppy as treatment for heart arrhythmias, but not malaria.  So I didn't feel so stupid then, but a still little bit ignorant compared with the native African healers who have been using this for over a century. The plant is native to tropical America, and was introduced into Africa sometime in the 19th century, which means the native healers there caught onto its medicinal properties fairly quickly!  We tend to think of traditional healers in general as following procedures cast in stone hundreds or thousands of years ago - a clearly unjustified stereotype.  In this instance at least, there were  intellectually flexible experimenters in the profession.

So what are the active principles in  prickly poppy tea? The Lewis text indicates a-allocrytopine obtained from the roots as the active principle in treatment of heart arrhythmia.  It also indicates that a more toxic mix of sanguinarine, berberine, protopine is present in the plants, and that prickly poppy occasionally contaminates grain.   This may be from the seeds of the prickly poppy, which have been implicated in poisoning events in India.  Sanguinarine is considered the primary culprit.

The leaves, however, have little sanguinarine, and the herbal tea, according to Borrell, is fairly non-toxic.  Isolated berberine has shown some anti-malarial effect, but much weaker than that of whole leaf infusions. So it is not known exactly what mix of compounds in the leaves is so potent against malaria.

Argemone mexicana might  turn out to be the tip of an iceberg.  There are 32 species in this genus, native mostly to tropical America, with one species in Hawaii.  Relationship among plants is highly predictive of similarity in secondary plant compounds.  These other species may have similar or even better combinations of compounds for treating malaria or other parasites.

This is not to mention the numerous other genera and species of the poppy family.  One must of course be very careful to steer away from the dangerous compounds found throughout this family, including the opiates in Papaver somniferum.  As I say on the first day of my medical botany course: "DO NOT TRY THIS AT HOME!"  Self-experimentation with natural plant compounds is exceedingly risky. If you can get a hold of the Lewis text, there is an excellent section on all the ways people inadvertently poison themselves.

The study of medicinal botany is both ancient and very new.  The new part is applying the modern scientific method to finding and verifying the curative or preventative properties of plant compounds.  The possibilities and opportunities in this field are endless.

References:

Borrell, Brendan.  2014.  Seeds of a Cure.  Scientific American 310 (#6): 64-69.

Lewis, W. H. and M. P. F. Elvin-Lewis. 2003.  Medical Botany, 2nd Ed., John Wiley and Sons.