ADDISONIA 37 
(Plate 19) 
OPUNTIA MACRORHIZA 
Large-rooted Prickly Pear 
Native of the south-central United States 
Family CACTACEAE Cactus Family 
Opuntia macrorhiza Engelm. Bost. Jour. Nat. Hist. 6: 206. 1850. 
Opuntia fusiformis Engelm. & Bigel. Proc. Am. Acad. 3: 297. 1856. 
Opuntia Rafinesquet fusiformis Engelm. Pacif. R. R. Rep. 4:43. 1857. 
Opuntia mesacantha macrorhiza Coulter, Contr. U. §. Nat. Herb. 3: 430. 1896. 
Opuntia xanthoglochia Griffiths, Rep. Missouri Bot. Gard. 21: 166, 1910. 
Opuntia Roseana Mackensen, Bull. Torrey Club 38: 142. 1911. 
A low cactus about a foot high or less, branching from the base, 
the branches nearly or quite prostrate, or ascending, forming clumps 
up to three or four feet in diameter. The roots are thick, tuber- 
like, often clustered, sometimes two inches in diameter or more. 
The flattened joints are obovate or nearly orbicular, dull green, 
from two inches to about six inches long, usually a little longer than 
wide and about half an inch thick, with slightly scalloped margins. 
The leaves, which as in most prickly pears away soon after 
appearing, are awl-shaped, pointed, half an inch long or less. The 
areoles, situated in the axils of the leaves, on the sides and the edges 
ovate-lanceolate, pointed, three quarters of an inch long or less; the 
yellow, with a red or purplish base. The numerous stamens are 
much shorter than the petals, with greenish or yellowish filaments 
and small, yellow anthers. The five or six nearly white or pale 
green stigmas are shorter than the slender style. The fruit, ripe in 
autumn, is narrowly obovoid, red or purplish, two inches long or less, 
half an inch to nearly one inch thick. The seeds are about one sixth 
of an inch broad, and margined. 
Opuntia macrorhiza has its nearest relatives in Opuntia austrina 
Small, of southern Florida, an erect species with strongly scalloped 
joints, and in Opuntia iortispina Engelm., which has a wide range in 
the central United States, and is usually much more spiny, and with 
fibrous roots. It is a member of the series Tortispinae, to which 
