Journal archives for October 2019

October 08, 2019

Euphorbia leaf colors and patterns


Euphorbia abramsiana.

Many species of Euphorbia produce odd patterns on their leaves. Some of these have led to their production as ornamentals, while others are more random.

Maculations
Euphorbia maculations come in many shapes and sizes. They vary across species and across sections but seem to be primarily restricted to subgenus Chamaesyce. Within sect. Poinsettia and sect. Alectoroctorum, the maculations are simply spots scattered on the leaves without much pattern. They are most common in the dentata group including E. dentata, E. davidii, and E. cuphosperma among others. Euphorbia cuphosperma, in particular, produces maculations abundantly. A couple other species include E. heterophylla, and rarely E. graminea.


Euphorbia cuphosperma.

Euphorbia davidii.

Euphorbia heterophylla. Photo credit: Martin Reith

Euphorbia graminea. Photo credit: Ruth Ripley

Within sect. Anisophyllum, the maculations become more consistent both in presence and in pattern. The maculations become so consistent that they can actually be used for identification under some circumstances. The maculations tend to come in four basic patterns. It should be noted that maculations are inconsistent by their very nature, but the patterns they produce are often distinctive. Also, most species lack the ability to produce maculations. This makes maculations valuable as a characteristic if they are present, but essentially useless if they are absent. Also, most species within sect. Anisophyllum lose their maculations during the fall. This can be contrasted with the members of sect. Poinsettia which seem to generally keep them or even make them more pronounced in the fall.

Centralized and continuous
This is the most commonly encountered and the type found in E. maculata (spotted spurge). This type also occurs in species like E. glyptosperma, E. serpillifolia, E. serrula, E. velleriflora, E. hirta, E. ophthalimica (in Mexico), E. albomarginata, and some others.


Euphorbia maculata.

Subcontinuous
This is only known to occur in E. abramsiana and rarely E. hyssopifolia. The pattern is characterized by an irregular shape roughly along the midrib often with additional spots outside. It appears as though it is made up of many smaller spots. In E. abramsiana, pale lines in the position of pinnate venation are also generally present.


Euphorbia abramsiana.

Euphorbia abramsiana; maculation type verging on scattered.

Scattered
Found only in E. taluticola, some populations of E. pediculifera, and seedlings of E. hyssopifolia and E. nutans (in part; see proximally restricted). It is characterized by round spots scattered throughout the leaves like is occasionally found in sect. Poinsettia.


Euphorbia pediculifera. Photo credit: Mike Plagens.

Euphorbia hyssopifolia seedling displaying scattered maculation pattern. Photo credit: Zoologist123.

Proximally restricted
This occurs in E. hyssopifolia and E. nutans. I have not seen it in any other species, but it may occur in their relatives in Central and South America. This pattern is quite unique in that seedlings that produce maculation typically produce scattered patterns or sometime subcontinuous. Later midstem leaves have maculations that are positioned in the middle of the proximal two-thirds of the leaves. The maculation is generally continuous or subcontinuous, but is often wider than other species with these types of maculations. There is also often a white line along the midrib distal to the maculation.


Euphorbia nutans displaying broad, continuous maculation proximal to broad white line along midrib. Photo credit: Rick Travis.

Euphorbia hyssopifolia displaying broad, continuous maculation. Photo credit: Joshua Doby.

Euphorbia hyssopifolia displaying narrow, continuous maculations. Photo credit: odandno.

Euphorbia hyssopifolia seedling displaying scattered maculation pattern. Photo credit: Zoologist123.

Euphorbia hyssopifolia young plant displaying scattered/subcontinuous maculation pattern. Photo credit: James Bailey

Colored bracts
These are the most commonly noticed and frequently occur in sect. Poinsettia and in sect. Alectoroctonum. There are three basic forms this takes.

Gradation of color from base of leaf
This is commonly found in the dentata group but also occurs in E. heterophylla. This is perhaps most pronounced in E. mayfeildii and E. scheidiana. Euphorbia radians also probably best falls under this category even though the majority of bracts are usually fully light pink.


Euphorbia scheidiana. Photo credit: Leticia Soriano Flores.

Euphorbia radians. Photo credit: Oscar González.

Restricted color regions
Most pronounced and well known in E. cyathophora and E. marginata. Instead of a more gradual transition from green to white or some other color, the regions are well defined.


Euphorbia cyathophora; note the dark region between the green and red parts of the leaf. Photo credit: meldrake.

Euphorbia marginata.

Bracts fully colored
Most prominently seen in E. pulcherrima and related species. See also E. leucocephala and cultivars of E. graminea. If gradations occur, whole leaves are intermediate and less often producing intermediate colors on the same leaves.


Euphorbia pulcherrima.

Euphorbia leucocephala. Photo credit: Neptalí Ramírez Marcial.

Bands or other patterns
Some species produce patterns other than maculations on their leaves. These are rare and there are only a few species I have seen them in. Euphorbia graminea and members of the complex (sect. Alectoroctonum) sometimes produce bands similar to those of some Amaranthus species.


Euphorbia graminea. Photo credit: scottsuth.

Euphorbia xalapensis. Photo credit: solecito.

The other conditions are found in sect. Anisophyllum. Euphorbia abramsiana produces pale lines in the position of pinnate venation and E. hyssopifolia and E. nutans often produce white lines along the distal two-thirds of the midrib.


Euphorbia abramsiana.

Euphorbia nutans displaying broad, continuous maculation proximal to broad white line along midrib. Photo credit: Rick Travis.

Notes on anthocyanins
Maculations and red bracts are made of reddish pigments called anthocyanins. These are not just restricted to leaves, but may occur in every other structure. The key to understanding their significance is to know that there is typically a strong environmental influence in combination with the genetic influence. In maculations and bracts, the environmental influence is weaker. This makes them more useful as identification characteristics. There does appear to be some genetic variability in the anthocyanin production in other regions (see discussion on stems here and photo here). But with the exception of cyathia which really deserve their own post, the variability is generally unpredictable. They are mostly just gradations from green to red. Briefly, cyathia anthocyanin concentrations often vary based on the structure. The glands typically have the greatest concentration while the appendages have the least. The involucre and flowers (including ovaries and fruits) are typically inbetween, but this does vary.

Posted on October 08, 2019 01:21 by nathantaylor nathantaylor | 4 comments | Leave a comment