Virgin Valley Formation
picture above shows both the primary and secondary cylinder. You
can clearly see the difference in the arrangement of vascular
bundles. The vascular bundles in the secondary cylinder
are much more orderly. The specimen below illustrates the transition
between the secondary cylinder and the periderm.
The secondary thickening meristem (STM) has eroded, but its former
location is noted.
I stand next to my grandmother Grace Furnish
My mom, Noni sits in our 1969 Datsun 510, while my dad, Wayne, takes the
Joshua tree forms scattered groves on arid mesas and
mountain slopes. It is widely distributed in the Mohave
Desert and is found in California, Arizona, and Nevada
(Elias, 1980, p. 910). Two coevolutionary relationships
have been important for the Joshua tree's reproduction,
one for fertilization and the other for seed dispersal.
During the last ice age Joshua trees were widespread
across the American Southwest.
cave in Clark County, Nevada holds clues to the past success
of the Joshua tree. In the 1930's skeletons, hides, hair
and dung of the giant ground sloth Northrotheriops
shastensis were discovered in Gypsum cave. Layers
of 13,000 year old dung revealed that the Shasta ground
sloth's favorite food were the leaves, fruits and seeds
of the Joshua tree. During the ice age giant ground sloths
provided a method of seed dispersal, via their droppings,
which positively influenced the geographic range of the
Joshua tree (Shogren, 2008). This type of seed dispersal
had the added advantage of providing a natural fertilizer.
Today the single surviving species of Joshua tree, Y. brevifolia, has a much smaller geographic
range. Still, the tree depends on an animal for its reproduction, specifically
for fertilization. The "Yucca Moth" Tegeticula synthetica has
an obligate pollination mutualism with the Joshua tree. The white female moth
visits the flowers when they open at night. She visits and collects pollen
from one tree and then visits another. The female moth deposits her eggs inside
the ovary of the flower. She then rubs the pollen on the stigma of the flower.
After completing the necessary cross-pollination the seeds develop and some
serve as food for the developing moth larvae (Bland & Jaques, 1978, p.
the Joshua Tree
then the largest Joshua tree in the world,
in 2005 with
her friend Frank Daniels.
Photo by Frank Daniels, (c) 2006-2013
R.G. and Jaques, H.E. (1978). How to Know the Insects [3rd
Ed.] Dubuque, IA: WCB McGraw-Hill
T.S. (1980). The Complete Trees of North America.
New York: Van Nostrand Reinhold Company.
E. (2008). Outlook Bleak for Joshua Trees. NPR
Tidwell, W.D. and Parker, L.R. (1990). Protoyucca shadishii gen. et.
sp. nov., An Arborescent Monocotyledon with Secondary Growth from the Middle
Miocene of Northwestern Nevada, USA. Review of Palaebotany and Palynology.
62, pp. 79-95.