gigantea (Englem.) Brit & Rose
by Mead Zaccagni
Mier, Native Plants Class 2003
Common names: Saguaro, Giant Cactus.
Synonymy: Cereus giganteus
Etymology: The Genus name comes from Andrew Carnegie
(1835-1919), an internationally renowned philanthropist. The common name,
Saguaro, is an Indian name (1).
Growth form: Considered a tree/ subshrub, the Saguaro is the
largest cactus in the US, commonly up to 12 m tall and with extremes of
23.8 m (5). It takes a bowling pin shape for about the first 35 years
until it reached around 2.5 meters. At about 65 years it has achieved
its maximum number of ribs and begins to branch. It can grow up to 50
Roots: Saguaro has a large tap root reaching 60 cm deep
with smaller shallow roots, less than 10 cm deep, reaching as far out
wide as the cactus is tall (3).
Stem: Fleshy tissue for water storage with ribs in center
(4,6). Green photosynthetic exterior with waxy skin that pleats in accordion
shape. Pleats expand for water uptake creating stems that can weigh 80
pounds per foot (3,4).
Leaves: Leaves are modified into clusters of white or
pink spines located every 2.5 cm on the outer ribs (2). The lower 2.4
m have hard spines while above that point they are more flexible and bristly.
There are up to 30 spines per areole and spines are up to 5 cm long (3).
Inflorescence/flowers: The Saguaro flower is the Arizona
state flower. Petals are spirally arranged and white. Flowers are 8 cm
in diameter, clustered on ends of arms, require cross pollination, and
have the aroma of “ripe melons” (3, 2). Flowers are pollinated
by bats and insects(3, 6).
Fruit: Saguaros propagate by seed. Juicy, red, oval-shaped
fruits ripen one month after flowers bloom (2). When ripe, the fruit splits
into 4 sections revealing over 2000 tiny, black seeds (2, 3).
Similar species: Carnegia is the only species in its
genus (5). There are 5 other species of Cereus, the past genus for this
species, in Arizona, none nearly as large as the Saguaro (2).
Life history: Perennial (5)
Native/introduced: The distribution of the Saguaro defines
the boundaries of the Sonoran Desert. Its range spans from western Sonora,
Mexico to southern Arizona and California. It is a tropically derived
plant with relatively recent evolutionary origin in Arizona (3, 4, 5)
Photosynthetic pathway: CAM
Phenology: Saguaros are long lived, averaging life spans
of 85 years, but can live up to 200 years (2). Most deaths occur during
the first year’s establishment. Flowers bloom in May to June just
before monsoons, opening at night and staying open until midday the next
day (3, 4).
Distribution: The elevation Carnegia gigantia is found
at is 183 m to 1100 m on rocky slopes and well drained flats (2). The
greatest abundance of Saguaro occurs in the Arizona Upland. In more northerly
ranges, Saguaro is frequently found on southern slopes. Its native range
borders tropics in warm arid deserts. Saguaros are cold intolerant, vulnerable
to fire in the more mountainous habitats, and also vulnerable to wind
and lightning (3,4 ).
Wildlife: Wood rats, bighorn sheep, and jackrabbits eat the stem
tissue. Birds of prey use the Saguaro for hunting perches and nesting
between arms. Other birds eat and help to spread the seed. Birds also
nest in holes in the stems, called boots, which were previously dug out
by woodpeckers and flickers (3, 4)
Human: Saguaros are protected by the US federal government
and are conserved in Saguaro National Park. The Tohono O’odam consider
the Saguaro another form of humanity. The Saguaro is a part of many of
their creation stories as well as the basis for the seasons of their calendar
year. Natives have traditionally used the Saguaro boots for storage, the
fruits for food and wine, the seeds for flour, and the ribs for fences
and houses (3).
1. Charters, Michael L. 2003. California Plant Names, Word Meanings and
Name Derivations. www.calflora.net/botanicalnames/index.
Sierra Madre, CA.
2. Epple, Anne Orth. And L.E. Epple. 1995. A Field Guide to the Plants
of Arizona. The Globe Pequot Press, Connecticut.
3. Phillips, Steven S and Patricia Wentworth Comus, Ed. 2000:A Natural
History of the Sonoran Desert. Arizona-Sonora Desert Museum Press, Tucson,
4. Stenbergh, Warren F. and Charles H. Lowe. 1983. Ecology of the Saguaro
III: Growth and Demography. Scientific Monograph Series, Number 7, US
Department of the Interior, National Park Service, Washingaton, D.C.
5. USDA, NRCS. 2002. The PLANTS Database, Version 3.5 (http://plants.usda.gov).
National Plant Data Center, Baton Roughe, LA 70874-4490 USA
6. Usher, George. 1996. A Dictionary of Botany. Constable & Company