Ironwood (Olneya tesota) pollen is tricolporate with "roughened"
(approaching reticulate) sculpturing. The pollen grain (ca. 37 (P) x 28 (E) µm) is rectangular in equatorial
view and round in polar view. The furrows are narrow and straight, and the polar area
is small. The furrows are flanked by broad sculptureless "margos."
The large endopores are not visible in SEM micrographs, but are visible with
careful LO analysis under transmitted light.
Ironwood (Palofierro) trees are common in the Sonoran Desert. The plants are frost sensitive and
occur (above the limit of cold air drainage) in the upper bajadas of desert basins in Arizona and
eastern California at the northern limits of the plant's distribution.
They bark of young branches is light,
but mature stems are dark and furrowed. The leaves are pinnately compound, and the
flowers are light purple. The wood is used for "ironwood carvings" - originally by the
Seri Indians of western coastal Sonora, but now by commercial enterprises chiefly in
the city of Hermosillo, Sonora.
Pollen light micrograph:
The rectangular outline and short straight furrows are distinctive, but LO analysis is often
needed to distinguish the large endopore. This furrow in the thin area over the pore may
be pinched, and the pore membrane may protrude. The "margo" is not obvious in
light microscopy. Olneya grains area readily distinguished from Prosopis
pollen (pollen-of-the-month Feb. 02)
Mesquite's pollen is less rectangular; it has a larger polar area; it's furrows are broader,
and it's endopore is smaller, surrounded by a annulus, and included within the edges of the furrow.
Pollen scanning electron micrograph (SEM)
The endopore is sometimes faintly visible.
Production and Dispersal:
Insect-pollinated ironwood has low production and poor dispersal, but the flowers are
occasionally very abundant, and pollen abundances pf over 15% may be found in modern
This branch of the Leguminosae (Fabaceae) is thought to have originated
in the neotropics during the Neogene. However, there are no fossils records
of the pollen older than Pleistocene, as far as I am aware.