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1911 | 


Bartlett,— Euphorbia arundelana 


1(53 


EUPHORBIA ARUNDELANA, AN ALLY OF EUPHORBIA 

IPECACUANHAE. 


Harley Harris Bartlett. 


I)r. Millspauoh has said that “the singular and extremely amor¬ 
phous’’ Euphorbia Ipccacuanhae “represents in itself seven ‘ Rafines- 
quian species,’ so greatly does it vary in form, color, inflorescence and 
leaf.’’ No one who has seen the plant in nature will dispute the 
statement. The leaves vary from linear to broadly ovate, and 
between two plants of the same leaf shape, growing in the same square 
foot of soil, there is often a difference of several hundred percent in 
the size of the leaves. Some plants are entirely purple, some pale 
green, in others the purple pigment is definitely localized in certain 
organs. A colony of Euphorbia I pecacuanhae consists of a host of 
forms, different enough from one another so that they can be assembled 
into groups of like individuals. De Vries' believes that the species 
is in a mutable condition. 

In the western part of Anne Arundel County, Maryland, there is a 
close ally of Euphorbia I prcacuanhae, seemingly undescribed, which 
may lx* called Euphorbia arundelana. Both species grow together 
in a small area (equidistant from the bridges which cross the Patuxent 
River to Laurel and Bowie, Prince George’s County) designated as 
“Sassafras fine sandy loam” 1 2 on the U. S. Soil Survey sheet of Anne 
Arundel County. 

The essential and striking character of Euphorbia arundelana is 


1 “ Herr Dr. .). \V. Harsh! )erger sandte mir Material von Hibiscus Afoscheutos und 
Euphorbia Ipecacuanha aus Pennsylvania, welches durch den auffallenden Reichthum 
an Formen auf eine Mutationsperiode fur diesen Arten schliessen lasst.” De Vries, 
Die Mutationstheorie, 11, p. 664. 

2 This soil type is a brownish or deep yellow sandy loam, heavy at the surface, but 
lighter in color and texture as the depth increases. “At 26 to 30 inches it passes into 
a sand or loamy sand varying in color from a light yellow to a reddish brown. . . . 
The loose open character of the subsoil allows excessive moisture to pass readily 
through it, while at the same time the texture of the soil gives it a good water-holding 
capacity. . . .The material composing the soil is a marine sediment washed down from 
the higher lands farther north....The particles are sharp and angular, indicating 
that the soil has not been water-worn to a great extent. . . .The Sassafras fine sandy 
loam occurs principally in the southern and western parts of the country.... It is 
found at elevations ranging from 40 to 150 feet above tide.” .1. C. Britton and C. R. 
Zappone, Soil Survey of Anne Arundel County, Maryland. (Advance Sheets — 
Field Operations of the U. S. Bureau of Soils, 1909.) 




I 


m 


Rhodora 


[July 


the presence of broad white appendages, often tinged with pink, on 
the involucral glands. E. Ipecacuanhae has often been described as 
having exappendiculate glands, but Norton 1 has pointed out that a 

narrow green appendage 
is always present. Partly 
on this ground he excluded 
the species from the sub¬ 



genus Tithymal wt. 


Dr. 


Fig. 1. Euphorbia arundelana. Expanded invol¬ 
ucre showing broad appendages. ( X 5) 


Small 2 transferred it to 

Tithymalopsis , and the 

discovery of E. arundelana 

shows that its affinity is 

really with the members 
%/ 

of this group. In E. Ipecacuanhae the appendage is so inconspicuous 
as to be easily overlooked, in E. arundelana, on the other hand, it is 
quite as conspicuous as in the familiar E. corollala. (Compare the 
text figures.) The range of variation seems to be as great in E. 
arundelana as in E. I pecacuanhae, but the 
two series of forms present the follow¬ 
ing contrasting characters. 1) Some 
forms of E. arundelana (not all) are pu¬ 
bescent. In Anne Arundel (ountv there 

4 

seem to be no pubescent forms of E. 

I pecacuanhae, nor are there any pubes¬ 
cent specimens of it in the National 
Herbarium. The presence of pubes¬ 
cence is therefore diagnostic; its ah- 



Fig. 2. Euphorbia I peca¬ 
cuanhae. Expanded involucre 
showing very narrow appen¬ 
dages. ( X 5) 


sence is not. 2) In the forms of E. arundelana the stems are prevail¬ 
ingly of strict, upright habit, whereas those of E. I pecacuanhae tend 
to be spreading or decumbent. In other characters the two species 
are strikingly alike. It is especially noteworthy that the finger-thick, 
deep, vertical roots are indistinguishable. 

Euphorbia arundelana sp. now Herba perennis habitu Euphor- 
biae I pecacuanhae simillitna. Radix perpendicu laris longissima 
crassitudine circa 1 cm., caulibus subterraneis multiramibus plus 
minusve tortuosis coronata. Caules plures floriferi annui, altissimi 


1 J. B. S. Norton. Report Mo. Rot. Hard. XI (1900). p. 80. 

2 J. K. Small, Flora Southeastern U. S., p. 1334. 





1911 ] 


Bartlett,— Euphorbia arundalana 


165 


2 dm. attingentes, deorsum altematim, sursum dichotome vel tricho- 
tome ramosi. Folia inferiora squamiformia alterna, superiora 
verticillata vel saepius opposita, summis exceptis quam internodia 
multurn breviora, amplitudine formaque valde varia, lanceolata vel 
ovata, mediocria circa 2 cm. longa, sessilia vel brevissime petiolata. 
Pedunculi erecti in dichotomiis (aut trichotomiis) terminales, quique 
involucrum unum ferentes, infimi usque ad 7 cm. longi internodia 
aequantes, summi foliis breviores. Involucrum hemisphaericum 
glandulis appendice lata patenti conspicua circumdatis. 

forma a omnino glabra, foliis cauliluisque viridibus; involucri 
glandulis albo-appendiculatis. 

forma (3 omnino glabra, foliis caulibusque purpureis; involucri glan- 
dulis roseo-appendiculatis. 

forma y caulibus, praecipue nodis, foliisque pilosis deinde glabratis, 
purpureis; pedunculis glabris, involucris extus circulatim ad scg- 
mentorum baseis pubescentibus, alibi glabris; glandulis albo-appen- 
diculatis. 

In fine sand, southeast of Laurel, Maryland, in Anne Arundel 
County, 1 May, 1910, Bartlett 1954 (form a), 1955 (f. /3), and 1956 

(f. y). The three forms which are defined illustrate the types of 
variation shown by this species. Other forms are represented by 
Bartlett 1952 and 1953; many more might have been collected. 

Since the soil in which Euphorbia arundelana grows is agriculturally 
the best in the region, its native flora is but poorly preserved. The 
Euphorbias occur in fence corners and in the narrow strips of undis¬ 
turbed sand between roads and farm fences. 

Bureau of Plant Industry, Washington, D. C.