Euphorbia species of the United States's News

June 14, 2019

Section Anisophyllum explained

The sandmat group (sect. Anisophyllum) of Euphorbia is quite different from the other groups. It is likely the most distinctive and has commonly been referred to by its own genus (most often and most recently Chamaesyce). It is probably most commonly known in North America for spotted spurge. I have written fairly extensively and technically about the differences, but I'm going to attempt to simplify it all here. If you are interested in the more technical explanation, you might try reading the morphology section of my thesis.

Spotted spurge (Euphorbia maculata).

C4 photosynthesis and Kranz anatomy
Perhaps the most consistant and interesting charactaristic is the presence of C4 photosynthesis, which occurs in all but subsect. Acutae (i.e., Euphorbia acuta, E. angusta, and E. johnstonii). Of course, you can't really see C4 photosynthesis, but there is a cool trick you can use to tell if a plant has C4 or C3 photosynthesis. C4 photosynthesis comes with specialized anatomy called Kranz anatomy where the primary photosynthesizing cells are clustered around the veins. This makes the veins look darker than the surrounding tissue creating an interesting pattern.

Kranz anatomy in Euphorbia prostrata.

Dorsi-ventral (sided) stems and unequal leaves
In most species, there is a clear upper and lower side to the stems (i.e., a sidedness; also known as dorsi-ventral because the stems have a dorsal and ventral side). This is most obvious in prostrate species but is present in most upright species too. Take for instance hyssop spurge (E. hyssopifolia), nodding spurge (E. nutans), or graceful spurge (E. hypericifolia). In all these cases, the stems are generally quite upright, but the stems bend toward the tips so that the upper sides of the branches face the sun (usually described as arcuate ascending). This sided appearance comes in part from the asymmetric nature of the leaves. One side of the leaf (as divided by the midvein) is almost always longer than the other side. This makes the leaves more efficient when they turn sideways and allows the lobe of the longer side (what I have sometimes referred to as the cordate lobe) to overlap the stem, but the other side not to be obscured by the stem. The plants are so well evolved for a prostrate lifestyle that their leaves are built to make the most of it. There are rare exceptions to this rule (look at E. acuta for example), but it is a quick and pretty reliable technique to distinguish from the other groups.

Arcuate ascending habit and dorsi-ventral positioning in E. hypericifolia (left). Greatly exagerated assymetric leaves in a E. glyptosperma seedling (right).

Non-glandular stipules
Stipules are structures made of leaf tissue that grow on either side of a petiole. In some species outside Euphorbia, these can become leafy, thorny, or even twining (some tendrils are modified stipules). In Euphorbia they are almost always small, inconspicuous structures or may be absent altogether. In sect. Anisophyllum, they are generally small and white and can be found between the pairs of leaves. Each leaf produces one on each side of the stem (one on the dorsal, one on the ventral). Each individual stipule may become lobed to the point of appearing like more than one structure or can fuse with the other leaf's stipule on its side of the stem to form a scale. Though this can be useful for ID within sect. Anisophyllum, the key is that they are almost always present and almost never glandular. This is what helps to distinguish them from other groups.

Laciniate stipules of Euphorbia glyptosperma (left). Stipules of E. albomarginata that are fused together into a single white scale (right).

Sympodial branching (pseudo-dichotomous)
The branching is also interesting in sect. Anisophyllum. Within the group, each branch produced terminates (either stops growing, aborts, or is terminated by a cyathium) and is followed up by a pair of branches. This looks very similar to dichotomous branching which produces the same forking at the nodes, but this is slightly different. In true dichotomous branching (which can be seen in the wisk fern, genus Psilotum), the apical bud itself splits into two equal buds. In sympodial branching, the apical meristem itself stops and branches take over in its sted. This has led to the term pseudo-dichotomous branching (i.e., false dichotomous branching).
For distinguishing from other members of Euphorbia, the key is that members of sect. Anisophyllum have this branching right down to the base. Its very first apical produces one pair of leaves and produces nothing else. The branches take over from there. In other Euphorbia groups, the inflorescences are often sympodial, but the vegitative stems are not. This has led to speculation that members of sect. Anisophyllum are the result of reduction of plants to only the inflorescence but this explaination as it has been traditionally proposed has faced some critisism, so I will not go into the details here. If anyone wants to learn more, I recommend Hayden (1988): Ontogeny of the Cotyledonary Region of Chamaesyce maculata (Euphorbiaceae). Regardless, this is another useful characteristic!

Sympodial branching and equal length in paired branches of E. golondrina (left). Seedling of E. glyptosperma showing blank, flat spot where the apical meristem would be in most other plants (right).

Ecarunculate seeds
Lastly, members of sect. Anisophyllum have seeds that aren't carunculate. A caruncle is an outgrowth at the part of the seed that attaches to the fruit called the hilum. Many members of Euphorbia have carunculate seeds, but not members of sect. Anisophyllum. The closest they come is in the species E. carunculata but despite the name, the enlarged structure is an outgrowth of the micropyle (the part of the seed where the pollen grew through), not the hilum. For this one, it's probably easier to explain with pictures than words. If you want the full explanation or to know how seeds can be used in identification, I recommend reading my advanced seed morphology explanation.

Ecarunculate seed of E. lata ("E" represents the hilum), sect. Anisophyllum (left). Carunculate seed of E. tetrapora, subgenus Esula (right).

Outgrowth of the micropyle in E. carunculata, sect. Anisophyllum (left).

Posted on June 14, 2019 05:39 by nathantaylor nathantaylor | 2 comments | Leave a comment

June 13, 2019

Varieties of E. deltoidea

E. deltoidea var. adhaerans

Photo credit (left): Jay Keller (click here for observation). Photo credit (right): Jay Keller (click here for observation).
iNaturalist observations, Flora of North America.

E. deltoidea var. deltoidea

Photo credit (left): Pablo L Ruiz (click here for observation). Photo credit (right): Jay Keller (click here for observation).
iNaturalist observations, Atlas of Florida plants, Flora of North America.

E. deltoidea var. pinetorum

Photo credit (left): Jay Keller (click here for observation). Photo credit (right): Jay Keller (click here for observation).
iNaturalist observations, Atlas of Florida plants, Flora of North America.

E. deltoidea var. serpyllum

Photo credit (left): Jay Keller (click here for observation). Photo credit (right): Jay Keller (click here for observation).
iNaturalist observations, Atlas of Florida plants, Flora of North America.

Flora of North America treatment to species.

Posted on June 13, 2019 16:36 by nathantaylor nathantaylor | 0 comments | Leave a comment

May 28, 2019

A few members of subgenus Esula sect. Helioscopia

These plants have serrated leaves and glands without appendages. According to Euphorbia PBI, there are about 180 taxa. To go through them all would be very time consuming and well beyond the scope of this project. However, in order to better understand the species that have been introduced to other locations, it is worth discussing a few outside the US that have spread outside of Afroeurasia where most species are native. Notes on leaves refer to the lower leaves and usually includes the similar pleiochasial bracts, but not the dichasial bracts (click here for notes on the bracts). Plants known to occur in New Zealand are marked "NZ" at the end. Plants known to occur in the United States are marked "US" at the end.

E. oblongata - Perennial; stems villous; leaves glabrous, ranging from oblong, elliptic, to broadly lanceolate or ovate, not linear or linear-lanceolate, typically broadest at the base or middle but may be broadest at the apices, apices rounded; glands typically 2-3 (typically 2 in dichasia); fruits warty. Originally from Eurasia, but introduced elsewhere. NZ US
E. depauperata - Perennial; stems glabrous or pilose; leaves glabrous or occasionally pilose, typically linear-lanceolate, sometimes slightly broader, apices typically acute; glands 4-6; fruits warty. Africa.
E. epithymoides - Perennial; stems villous; leaves pilose; broadest towards the middle or base, apices rounded; glands 2-5 (even in same inflorescence) but most commonly 4; fruits covered with many narrow, hair-like warts. Originally from Eurasia, but introduced elsewhere. US
Annuals - Many of these are quite difficult to distinguish and may require seed characteristics.
E. platyphyllos - Annual; stems usually glabrous; leaves glabrous or hairy, usually oblanceolate, typically broadest at apices, apices acute; many dichasia produced before terminal pleiochasium of 3-5 branches; glands 4; fruits warty; seeds smooth, over 2 mm long. Two forms: 1. plants glabrous, more common. 2. plants hairy, less common (specimen 1; photos). Type much more robust than most specimens representing the species. Originally from Eurasia, but introduced elsewhere. NZ US
E. stricta - Annual, glabrous; leaves usually oblanceolate, typically broadest at apices, apices acute; many dichasia produced before terminal pleiochasium of 3-5 branches; glands 4; fruits warty; seeds smooth, under 2 mm long. Two forms: 1. leaves sharply acute, margins sharply serrulate; dichasial bracts mucronate; fruits warts shorter (specimen 1; specimen 2). 2. leaves less sharply acute, margins less sharply serrulate; dichasial bracts mucronate or commonly not; fruit warts long (photos; specimen). Misidentifications? Originally from Eurasia, but introduced elsewhere. NZ
E. spathulata - Annual, glabrous; leaves usually oblanceolate, typically broadest at apices, apices acute; glands 4; fruits warty, warts short; seeds reticulate. Seemingly restricted to North America, widespread. US
E. alta - Annual, glabrous; leaves usually oblanceolate, typically broadest at apices, apices acute; glands 4; fruits warty, warts long; seeds reticulate; restricted to SW United States and NW Mexico. US
E. texana - Annual, glabrous; leaves usually oblanceolate, typically broadest at apices, apices acute; glands 4; fruits smooth; seeds reticulate. Restricted to E Texas and Louisiana in the United States. US
E. helioscopia - Annual, glabrous; leaves usually obovate, broadest at apices, apices rounded or truncate; glands 4; fruits smooth. Originally from Eurasia, but introduced elsewhere. NZ US

Other species:
E. apios: link 1
E. hirsuta: link 1
E. palustris:
E. pterococca: link 1
E. valerianifolia: Fruits sparsely long pilose; link 1

Notes on E. oblongata/depauperata.

Posted on May 28, 2019 17:41 by nathantaylor nathantaylor | 0 comments | Leave a comment

May 06, 2019

The eastern members of sect. Alectoroctonum

Here, I am considering the species in states east of Texas. Observations from the area.

Euphorbia marginata

Photo credit: Sam Kieschnick (click here for observation).

Euphorbia graminea

Photo credit (left): Jay Keller (click here for observation). Photo credit (right): Jay Keller (click here for observation).

Euphorbia polyphylla

Photo credit (left): Jay Keller (click here for observation). Photo credit (right): Jay Keller (click here for observation).

Euphorbia ipecacuanhae

Photo credit (upper left): Rob Van Epps (click here for observation). Photo credit (upper right): Michael Ellis (click here for observation).
Photo credit (lower left): Jason Hafstad (click here for observation). Photo credit (lower right): Joshua Tewksbury (click here for observation).

Euphorbia exserta

Photo credit (left): ericpo1 (click here for observation). Photo credit (right): Jay Keller (click here for observation).

Euphorbia mercurialina

Photo credit (left): Erin Faulkner (click here for observation). Photo credit (right): Jonathan (JC) Carpenter (click here for observation).

Euphorbia curtisii

Photo credit (upper left): Andy Newman (click here for observation). Photo credit (upper right): jtuttle (click here for observation).
Photo credit (lower left): whiteoak (click here for observation). Photo credit (lower right): whiteoak (click here for observation).

Euphorbia hexagona

Photo credit: Brush F (click here for observation).

Euphorbia corollata complex
The photos bellow appear to represent true examples of their respective species. However, many populations are very difficult to determine. Some seem intermediate while others seem to represent distinct entities. There is at least one undescribed species represented in this group.

Euphorbia discoidalis

Photo credit (upper left): cwarneke (click here for observation). Photo credit (upper right): howardhorne (click here for observation).

Euphorbia pubentissima

Photo credit: Janet Wright (click here for observation).

Euphorbia corollata

Photo credit (upper left): Janet Wright (click here for observation). Photo credit (upper right): Alvin Diamond (click here for observation).
Photo credit (lower left): Kit Howard (click here for observation). Photo credit (lower right): Nathan Taylor (click here for observation).

References to look into:

Posted on May 06, 2019 04:23 by nathantaylor nathantaylor | 0 comments | Leave a comment

April 21, 2019

Advanced Seed Morphology

Seed morphology is very important to the taxonomy of the genus Euphorbia. It is so important that most larger keys require looking at the seeds. The seeds are so diagnostic that there are many instances where species can be determined just by looking at the seeds alone. Because of this, I think it's time that I write a little bit about the more complicated aspects of Euphorbia seed morphology. This does not cover the full variability of seed morphology but is intended to give an introduction to help you understand the terminology.

In almost every Euphorbia seed, there are four more or less flat sides (referred to here as faces). Two of these are generally longer than the other two as shown below.

These are useful for identification, but in order to understand the morphology of the seeds, there are some other characteristics that should be taken into account. First off, the faces are best identified in their relationship to the four angles. Look at the figures below.

Left and Right: A: distal angle (angle furthest from center of fruit); B: lateral angles; C: proximal angle (angle nearest center of fruit; also called the raphe). Left only: D: testa (seed coat); E: mucilagenous coat (only the white part). Right only: D: chalazal end; E: hilum (micropyle visible as brown dot directly right of hilum).

The two faces adjacent to the distal angle are known as distal faces. The two angles adjacent to the proximal angle are known as proximal faces. There is considerable variation in these faces between species. In some, the faces bulge so much or the angles compress so much that the faces are nearly indistinguishable from the angles and the seeds become essentially round in cross-section. In some, these faces are compressed and create somewhat deep depressions between the angles. The topography of the angles varies too. They may be ridged, wrinkled, pitted, papillate, or have some variation of these. In some species, it is important to know whether the ridges overlap the angles. Some have sharper ridges than others.

Aside from faces and angles, the figures above also identify the testa (the seed coat), the mucilaginous coat (the part that makes the coat slimy/sticky when wet), the chalazal end (defined as the end of the raphe opposite to the hilum), the hilum (place where the seed was attached to the fruit), and the micropyle (place where the pollen entered into the ovule during fertilization). Many of these exhibit variability between species that make them diagnostic. A characteristic not shown in the above figure is a caruncle (an outgrowth of the hilum), which can be useful for identification.


Euphorbia carunculata with an outgrowth of the micropyle. Source observation.

Euphorbia lata showing connections between hilum, micropyle, and fruit tissue. Source observation.

Euphorbia alta seed with caruncle. Source observation.

Euphorbia roemeriana displaying caruncle and enlarged chalaza. Source observation.

Seeds of various species showing diversity in ridges. Top left: E. serrula; top right: E. simulans; bottom left: E. prostrata; bottom center: E. glyptosperma; bottom right: Euphorbia theriaca var. theriaca.

Posted on April 21, 2019 20:44 by nathantaylor nathantaylor | 6 comments | Leave a comment

April 09, 2019

Euphorbia, What to Photograph?

I've heard it mentioned a couple of times that it helps a lot for people to have an idea of what they need to photograph. Hopefully, this will help.

1. Habit.
This is tied for the most important thing to photograph. If the photo is clear, all the essential characteristics will be visible in one or two good habit shots. In plants that lie flat along the ground, this only needs to be a top-down photo. In something that is upright, it's important to get a top-down photo and one from the side or potentially one at an angle in-between.

2. Branches.
Stems with leaves, flowers, and fruit if present. This one is just as important as habit. This allows for seeing a lot of major characteristics including leaves, phyllotaxy, stipules, cyathia, and sometimes fruit.

3. Undersides of leaves and/or branches (generally optional).
This helps with some groups and may help one see styles which are important in a few species. This can be particularly helpful for the species that lie flat along the ground.

Close-ups of the characteristics themselves (all usually optional):

Depending on what group you photograph, there may be more than one type of leaf. This is particularly important in subgenus Esula, which have the typical leaves and then two types of bracts. Many members outside subgenus Esula have leaves that are different when growing under a cyathium. When this is the case, it can be useful to photograph all different types. It's always best to get photos of both sides of the leaves, though usually not necessary in the US members of the genus Euphorbia.
Species where this level of detail may be helpful: members of subgenus Esula, E. bicolor, E. marginata, possibly E. dentata, and possibly E. davidii.

Small triangular (often membraneous) structures between two pairs of leaves in section Anisophyllum. Stipules are technically made from leaf tissue at the base of the petiole. Stipules vary from being entire to deeply lobed or even fused with its neighboring stipule. These may be hairy or non-hairy. In some, they are even reduced to simple glands.
Species where this level of detail may be helpful: members of section Anisophyllum.

Morphology explained simply here. Diversity in cyathial form within Euphorbia is vast. Though not always necessary for an ID, the uniqueness of these structures make them fun to photograph. Nearly every aspect of the cyathium may differ between species, but the most readily visible and often most useful diversity can be found in the glands and their appendages. The number of glands can vary from 1 to 5, and typically not 2 or 3 (rarely, plants will produce 2, 3, 6 and very rarely more glands). The gland ornaments can be petal-like, horn-like, or absent. If petal-like, they can be divided or undivided. They are usually white but can be pink, red, or (if horn-like) even yellow. These characteristics are usually visible from the branch photos but are fun to look at more closely.
Species where this level of detail may be helpful: essentially all, though especially E. arizonica, E. setiloba, E. spathulata, E. texana, E. ocellata and look-alikes, E. missurica, E. parryi, and eastern species of section Alectoroctonum.

Fruits and styles.
The fruits are not quite as variable as cyathia but are no less important. Fruits may be hairy or not hairy; warty, papillose, or smooth; and/or deeply lobed or subtriangular in cross-section. The three styles found at the apex of the fruit and maturing ovaries usually have two branches which may be divided all the way to the base, not divided at all, or be divided somewhere in-between.
Species where this level of detail may be helpful: essentially all.

Though difficult to photograph and only completely essential to identification in a couple of species pairs in the US, the seeds can be really important to identification. If you are unfamiliar with the group and have to key them out, you essentially must look at seeds. Seeds may be smooth, ridged, papillose, pitted, carunculate, ecarunculate, quadrangular, or round. Tips for extracting and photographing seeds can be found here.
Species where this level of detail may be helpful: essentially all, though especially E. simulans, E. theriaca, E. hyssopifolia, E. nutans, E. serpillifolia, E. glyptosperma, E. dentata (preferably with scale), E. davidii (preferably with scale), E. pubentissima (with scale), and E. corollata (with scale).

Posted on April 09, 2019 20:43 by nathantaylor nathantaylor | 0 comments | Leave a comment

January 14, 2019

Cyathium dissection and explanation

Today, I decided to delve into the morphology of the poinsettia cyathium (Euphorbia pulcherrima). For those unfamiliar with a cyathium, you should probably read this introduction to poinsettia morphology first. The observation and full set of photos for this dissection can be found here.

First off, here is a poinsettia cyathium and just like all other members of the genus Euphorbia, it has white milky sap. The sap can be seen when a cyathium is cut off.

The stalk that the cyathium sits on is called the peduncle. The big yellow part is called the gland. The small reddish things coming out of the tip are the staminate flowers. The fringed parts under the staminate flowers are involucral lobes and rudimentary cyathial glands (more on these later).

The involucre
The involucre, or cyathial wall, is thought to be made up of five fused bracts (though each gland has two prominent vascular bundles) which each bare an apex and a gland. The apex of the leaf is called an involucral lobe. In poinsettia, it is difficult to show all this because the involucral lobe is laciniate (fringed to the point of having several narrow lobes) and there is only one gland. The reason poinsettia has only one gland instead of the more typical five is that the four other glands were reduced into lobe-like outgrowths that look similar to the involucral lobes. To explain this, I'll first show a photo of Euphorbia missurica.

Source observation:
Note the triangular lobes between the glands and the single linear lobe at the far left (the involucral lobe at the far right was destroyed but was where the large cut out is now between the right two glands). The single linear lobe is the rudimentary "5th" gland. Now, here is a photo of the poinsettia involucre (left: outside; right: inside).

Note how on the photo of the internal view, there are alternating areas below the apex. There are areas with extra tissue (white) which extend forward into the center of the cyathium. These areas represent the bases of the glands. The areas that look more leaf-like represent the bases of the leaf area.

Bractioles and fascicles
The light-colored area mentioned above is special. The tissue that comes out here separates the staminate flowers into five clusters known as fascicles. These partitions become fringed towards the middle or tips and have been called bracteoles. If each can truly be called a bracteole, they represent the bracts of the staminate flowers. Time for photos. The one on the left represents two staminate fascicles surrounded by bracteoles (connate below; divided above). The one on the right represents a cross-section of a cyathium showing the five fascicles and the bracteolar tissue separating each one. Note how it is a fused structure completely surrounding all of the fascicles except where it touches the involucre. It also surrounds the pedicel of the pistillate flower (the gynophore) which is the round structure in the center.

There are also bracteole-like structures that originate at the bases of androphores instead of the bases of fascicles.

It isn't completely clear how these structures should be interpreted, but likely represent another set of bracteoles (rudimentary bracts).

The staminate flowers sit atop pedicels called andophores or andropeds. There is a clear line where the androphore ends and the flower begins.

The pistillate flower is abortive in the plant I have.

How to make cyathium dissections

When doing a cyathium dissection, it is important to either ensure that the cyathium/plant is not turgid (i.e., wilting), has been left sitting for a while so that it isn't turgid when cut, or has been rehydrated after drying (by putting in water with a small dollop of soap). If one of these steps aren't taken, the sap will obscure some of the structures, will stick to your hands, and can cause a safety problem should you rub your eyes after getting the sap on your fingers.

There are several pieces of information that are good to obtain while doing a dissection. For identification and description, it is useful to get the number of staminate flowers per cyathium, number of staminate flowers per fascicle, involucral internal vestiture, description of involucral lobes, and description of glands and rudimentary glands. Gynophore length (and sometimes androphore length) can be useful too but are usually very easy to obtain with very simple dissection.

The most informative shot is a photo of the inside of the cyathium from the center with and without staminate fascicles in the way (left: with fascicles; right: without fascicles).

The reason for this is that it accurately represents the morphology of the glands that can't be observed from the outside, the shape of rudimentary glands, the shape of the involucral lobes, and the hairs (or absence of the hairs) within the involucre. This should be done first to maximize the use of the cyathium.
To make the cut, one should first cut off the peduncle a little above the base of the cyathial wall (as shown at right above) so that the flowers (staminate and pistillate) are all free. After that, a cut must be made in the cyathial wall. It is usually best to cut just next to a non-rudimentary gland if possible and cut to the base (I have cut in different places in this photo series for showing other parts of the morphology). The cyathium can be spread out, put under a coverslip and photographed (both sides are ideal. After getting the shot with the fascicles, gently pull the fascicles out from the cyathium wall, put under a coverslip and shoot again.

The fascicles that are pulled away from the involucre can then be dissected. It is simple enough to just pull and pinch it apart. The staminate flowers can then be counted. The most accurate count will come from old cyathia that have few or no anthers. Under a microscope, the androphores can be differentiated from the bracteoles by being generally wider, their consistent cylindric shape, and prominent vascular bundles.

In case anyone is wondering why I'm writing this and using Euphorbia pulcherrima for the example, I am doing so for three reasons. 1. It is popular and well known by the general public which facilitates educational opportunities. 2. It has large cyathia which make dissection easy. 3. It is easily obtainable. Though E. pulcherrima is a bit over commercialized for my taste, the educational opportunity it brings with it is great. I hope that this gives you a new perspective on the species that facilitates learning more about Euphorbia and even botany in general.

Posted on January 14, 2019 03:08 by nathantaylor nathantaylor | 2 comments | Leave a comment

December 28, 2018

Statistics tracked

New observations per year:
2010: 2
2011: 18 (total: 20)(x9)
2012: 56 (total: 76)(x3.11)
2013: 158 (total: 234)(x2.82)
2014: 382 (total: 616)(x2.42)
2015: 1,086 (total: 1,702)(x2.84)
2016: 2,004 (total: 3,706)(x1.85)
2017: 4,535 (total: 8,241)(x2.26)
2018: 10,586 (total: 18,881)(x2.33)
2019 (incomplete; 23 May): 4,194 (total: 23,075)(x)

New species per year:
2010: 2
2011: 11 (total: 13)
2012: 12 (total: 25)
2013: 18 (total: 43)
2014: 22 (total: 65)
2015: 25 (total: 90)
2016: 14 (total: 104)
2017: 26 (total: 130)
2018: 7 (total: 137)
2019 (incomplete; 2 May): 10 (total: 147)

Breakdown by group (observations)
Anisophyllum (Subg. Chamaesyce)
2010: 1
2011: 6 (total: 7)
2012: 18 (total: 25)
2013: 51 (total: 76)
2014: 140 (total: 216)
2015: 569 (total: 785)
2016: 1,059 (total: 1,844)
2017: 2,583 (total: 4,427)
2018: 5,951 (total: 10,378)
2019 (incomplete): (total: )

Alectoroctonum (Subg. Chamaesyce)
2011: 6
2012: 18 (total: 24)
2013: 46 (total: 70)
2014: 89 (total: 159)
2015: 188 (total: 347)
2016: 391 (total: 738)
2017: 727 (total: 1,465)
2018: 1,685 (total: 3,160)
2019 (incomplete): (total: )

Poinsettia (Subg. Chamaesyce)
2010: 0
2011: 1 (total: 1)
2012: (total: 3)
2013: (total: 20)
2014: (total: 50)
2015: (total: 162)
2016: (total: 338)
2017: (total: 779)
2018: (total: 2,009)
2019 (incomplete): (total: )

Subgenus Euphorbia
2014: 1
2015: 0 (total: 1)
2016: 1 (total: 2)
2017: 5 (total: 7)
2018: 44 (total: 51)
2019 (incomplete): (total: )

Subgenus Esula
2010: 1
2011: 4 (total: 5)
2012: (total: 23)
2013: (total: 64)
2014: (total: 178)
2015: (total: 374)
2016: (total: 708)
2017: (total: 1,420)
2018: (total: 3,217)
2019 (incomplete): (total: )

Posted on December 28, 2018 20:31 by nathantaylor nathantaylor | 0 comments | Leave a comment

December 22, 2018

The Poinsettia

The red cultivated poinsettia, which goes by Euphorbia pulcherrima, is a native of central Mexico and extends southward into South America. But Christmas poinsettias don't just come in red. Various cultivars have been bred from hybridizing the red poinsettia with a white species of poinsettia, known as Euphorbia cornastra, which is restricted to southwestern Mexico in the state of Guerrero. A full display of what cultivars have been bred, a good set of photos can be found here. But, aside from the bright red or white leaves, the wild plants don't look as much like the poinsettia in your home. In Mexico, they often become small trees! Here are a couple photos of E. pulcherrima.

Photo credit (left): victor_evg. Photo credit (right): Laura Uribe.

And you know those large red things on the plant, they're actually not petals. Those are actually modified leaves called bracts. And those small things in the center? You're getting closer, but those aren't technically flowers either. Those tiny things in the center actually each represent a cluster of flowers (inflorescences) surrounded by yet more modified leaves. Here's a closer look at a different plant:

Photo credit (left): Daniel Buenrostro.
Photo credit (right): Oliver Komar.

So, if those little nubs are clusters of flowers, what are the actual flowers? And what is this weird yellow round thing coming off of the flower cluster? What about the red bristly things that are yellow tipped? Before I answer those very good questions, I need to explain a little more about the overall morphology. Each cluster of flowers is enclosed by modified leaves (remember, these are called bracts) that are fused together to form a cup-shaped structure. This collection of bracts is collectively called the involucre. This surrounds the many flowers inside. And that yellow thing with liquid in it? That is a gland produced by the poinsettia. This produces nectar to attract insects. The entire thing is referred to as a cyathium (pl. cyathia). Here is a close-up of the cyathium of a related species (Euphorbia davidii):

Photo credit (left): Nathan Taylor.

The flowers may be male or female. Botanists refer to male flowers as staminate (because they produce stamens, which produce pollen) and female flowers pistillate (because they produce pistils which turn into fruits which inclose seeds). In poinsettia plants and Euphorbia in general, each cluster of flowers (remember, this is called a cyathium) produces one female (pistillate) flower in the center and many male (staminate) flowers surrounding the female flower. Both the female and male flowers are on there own stalks called peduncles or pedicels. I think it's time for a picture:

Photo credit (left): Nathan Taylor.

Well, now that you've been given this information, let's review. The red things are modified leaves called bracts, the nubs in the center are the flowers surrounded by modified leaves that are all fused together, and only within these modified leaves do you get the flowers. Complicated? Yep, Euphorbia is like that, but it makes things fun. If you want to learn the structures in even greater detail, I recommend checking out the information at Euphorbia PBI or this journal post discussing the internal morphology of the poinsettia cyathium specifically.

Now that you've hopefully learned something, it seems a bit unfortunate that you can't really see poinsettia in its full splendor in the US. However, it does have relatives here that are native. Perhaps the most similar to the Christmas poinsettia is a plant commonly known as wild poinsettia (Euphorbia cyathophora):

Photo credit (left): marytmn. Photo credit (right): Pam Kleinsasser.

Despite the similarity in name, the christmas poinsettia was not cultivated from wild poinsettia as some sources suggest. Another relative is sun spurge (Euphorbia radians), a less common, but no less interesting species:

Photo credit: nancygdi.

Most of the other related species are less showy. However, they are interesting in their own way. Take beetle spurge (Euphorbia eriantha) for instance. If you look at the photo below, you'll notice that the gland isn't cupped like the others. That's because it has narrow appendages that came out of the gland that covers it up. Why it does this is a bit of a mystery, but perhaps it helps to conserve water in the desert environments that it lives in.

Photo credit (left): ventura. Photo credit (right): Fred Melgert / Carla Hoegen.

Here's another. The scientific name is Euphorbia heterophylla, but the common names that it is given don't often make sense. For instance, Mexican fireplant is one and some others it shares with wild poinsettia (E. cyathophora). The reason is that E. heterophylla has often been confused with E. cyathophora (wild poinsettia). But I'll tell you the secret to distinguish the two. Euphorbia heterophylla will never have red on the leaves and may even have a bit of white. Even more importantly, do you remember the gland I talked about before? Well, in E. heterophylla, this is circular. In E. cyathophora, this gland is oval or oblong (at least, north of the southernmost part of Mexico). In E. heterophylla, they are circular. This is very important because E. cyathophora may lack the red coloration under certain conditions and some areas (particularly in central to north-central Texas). Here's a comparison of Euphorbia heterophylla and E. cyathophora glands so you won't forget:

Left: Euphorbia heterophylla, photo credit Nathan Taylor. Right: E. cyathophora, photo credit Jay Keller.

The last species I will discuss is actually somewhat weedy. It is called David's spurge (Euphorbia davidii) and depending on where you live, you might find it growing as a weed in your yard. It has two relatives that can be nearly indistinguishable from it, toothed spurge (Euphorbia dentata) and hairy-fruit spurge (Euphorbia cuphosperma). Here is a picture of David's spurge:

Photo credit (both): Nathan Taylor.

The differences between the three species are small and can be difficult to discuss without causing confusion, so I won't go into it here. However, what I want to point out is that you might be able to find one of these species growing wild nearby! I encourage you to go out and look for one of or all of these interesting species and compare it to the poinsettia in your own home. What are the similarities? What are the differences? When you're done, you might try to find another species of Euphorbia that I haven't mentioned and do it again. All of poinsettias close relatives can be found here if you want to learn more. Happy hunting!

Just for fun, here are a few more pictures of the native species in their late-season splendor.

Euphorbia davidii. Photo credit (both): Nathan Taylor.

Euphorbia eriantha. Photo credit (both): Nathan Taylor (second photo).

Other links:
Cyathium dissection and explanation
Euphorbia PBI cyathium explaination
Project recommended resource list

Posted on December 22, 2018 00:04 by nathantaylor nathantaylor | 3 comments | Leave a comment

November 23, 2018

Euphorbia PBI subgeneric classification

For any of the curators who have been working on Euphorbia, Euphorbia PBI has a data portal where essentially all the species have been assigned subgeneric classification (under description). I've been working through the majority of the species as I find them and should have gotten all the North American species that have been added so far and have been slowly working through others. All this to say, there is a single source where the information can be referenced if you are interested.

Here's the link:

Posted on November 23, 2018 16:17 by nathantaylor nathantaylor | 5 comments | Leave a comment