WHAT IS HAPPENING 
TO THE HAWTHORNS? 
Half a Century Ago Only Ten Species Were Recognized in North America, Now 
There Are More Than 700—Several Lines of Evidence Indicate That 
Many of the New Forms Are Not New Species but Natural Hybrids 
L. M. STanpDIsH 
Botanical Laboratories of Harvard University, Cambridge, Mass. 
HOSE interested in the origin of 
species cannot afford to overlook 
Crataegus, the hawthorn genus, 
on account of the extraordinary 
multiplication of species in that genus 
during the last fifty years. Gray’s 
Manual of Botany in 1867 records ten 
species and four varieties; in 1869 his 
classification is the same, while Focke in 
Engler and Prantl’s ‘Die nattrlichen 
Pflanzenfamilien” gives only thirty or 
forty species for the whole North Tem- 
perate zone. Since 1900, however, the 
increase in the number of species of the 
genus has been enormously rapid. In 
1901 Britton’s Manual for the northern 
states west to the hundredth meridian 
records thirty-one species; in 1903 
Small’s Flora of the southeastern United 
States of America gives 185; in 1905 
Sargent’s Trees of North America, 132; 
while Gray’s New Manual, published 
in 1908, describes sixty-five species and 
fifty varieties. In 1910 those who had 
discovered the new forms were N. L. 
Britton, eight species and two varieties; 
W. W. Eggleston, ten species and three 
varieties; C. D. Beadle, 144 species; 
W. W. Ashe, 165 species, and C. S. 
Sargent, 524 species and six varieties. 
This unusual state of affairs was 
noticed by H. K. Brown (1).! In 1910 
in the Bulletin of the Torrey Botanical 
Club (page 152), he published an ac- 
count of his investigation of the subject 
in an article entitled ‘The Genus 
Crataegus and Some Theories of the 
Origin of Species.”” He had written to 
the leading authorities: C. S. Sargent 
of the Arnold Arboretum; C. D. Beadle, 
Director of the Biltmore Herbarium; 
W. W. Eggleston of the New York 
Botanical Gardens; Ezra Brainerd of 
Middlebury College, Middlebury, Vt., 
and Mr. Dunbar of the Park Depart- 
ment, Rochester, N. Y., and asked them 
a series of questions hoping to get their 
opinion as to the cause of the extraor- 
dinary multiplication of species in the 
last fifty years. 
The question that headed his list 
was: ‘Why did not the systematic 
botanists discover the large number of 
species of Crataegus years ago?’ The 
answers that he received were varied in 
the extreme. Sargent thought that 
their search was not sufficiently thor- 
ough; Ashe that they only used dry 
material; Beadle that their work was 
largely herbarium work; and Brainerd 
that they held in those days broader 
conceptions of what constituted a 
species. 
The next question on Brown’s list 
was: ‘Do you consider that the species 
now being described are elementary 
species?” The general consensus of 
opinion was that most of them were new 
species while some of them were mere 
fluctuations, and some were forms that 
have already been described and have 
escaped notice on account of the large 
numbers of new species in the genus. 
SAID TO BREED TRUE 
For his next question Brown asked: 
“Do these species breed true?’’ Sargent 
had planted over 3,000 numbers of 
seeds, and so far had found no evidence 
that they did not; the others agreed 
! The numbers in parentheses refer to the list of authors cited at the end of this paper. 
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