Excerpts from Jim Conrad's
Naturalist Newsletter

Pink Mimosa, MIMOSA BOREALIS, flowering

from the the April 21, 2013 Newsletter issued from the Frio Canyon Nature Education Center in northern Uvalde County, southwestern Texas, on the southern border of the Edwards Plateau, USA
PINK MIMOSA FLOWERING

On rocky slopes of the limestone hills framing the valley of the Dry Frio River nowadays you spot little explosions of bright pink amidst outcropping white rocks and greening clumpgrass. The half-inch wide (15mm) spheres of pinkness are clusters of good-smelling flowers borne on arching, thorny, soft-woody, knee-high "briar stems," as shown above.

Below you can see a close-up of individual flowers in a head shows that the powder-puff effect is produced by stamens with pink filaments and yellowish white, pollen-producing anthers emerging from each inside each corolla:

Pink Mimosa, MIMOSA BOREALIS, close-up of individual flower

The stems' leaves are twice compound in the manner of locust and acacia trees, because like those species this is a member of the vast Bean Family. It's a mimosa, one often called Pink Mimosa, Fragrant Mimosa or -- like so many other woody shrubs with curved spines -- Catclaw. It's MIMOSA BOREALIS, occurring on rocky hillsides and canyon slopes from southwestern Kansas and southeastern Colorado south into arid northern Mexico.

In this part of the world, if you see a plant with such flower heads and twice-compound leaves, its stem is woody, its leaflets are small (less than half an inch long, 15mm), and from each individual flower ten or fewer stamens emerge, it's one of several possible species of Mimosa. If it were an Acacia, the flowers' stamen number would be ten or more.

Because the species' flowers are so fragrant, nicely colored and attractive to pollinators, and the plant survives on little water, it's a welcome addition in this area's rock gardens, and deserves to be planted more with xeriscaping in mind. It can be grown by collecting seeds in the fall and sowing directly where you want them.


from the July 13, 2014 Newsletter issued from the Frio Canyon Nature Education Center in the valley of the Dry Frio River in northern Uvalde County, southwestern Texas, on the southern border of the Edwards Plateau, USA
PINK MIMOSA FRUITING

At about belly height, leaning from a bushy fencerow in Cooks Slough Nature Park on the south side of Uvalde, down on the Coastal Plain, some unusual fruit pods caught my attention because of their paleness against a dark green background of leaves, and because they were shaped so unusually, as shown below:

Pink Mimosa,  MIMOSA BOREALIS, legumes

These being flattish bean pods, and the compound leaves consisting of small leaflets, I figured we had a member of the Mimosa Tribe of the big Bean Family. Notice how the pods dangle in clusters. The really unusual feature, though, is how few beans were contained in each pod -- only two or three per pods -- and how deep are the sinuses between the bean-bearing segments. The temperature was in the mid 90s and I was blinded by sweat and cataracts, so I managed to photograph an apparently drought-stunted leaf not displaying the neat symmetry such twice-compound leaves should. Still, it displays the leaflets' shape and venation as you can see below:

Pink Mimosa,  MIMOSA BOREALIS, leaf

With such unusual but well formed pods, or legumes, the bush or small tree revealed itself as one of several woody species going by the name of Pink Mimosa, because of its pink flowers. It's MIMOSA BOREALIS, which we've already profiled in flower.

Maybe because Mimosa borealis isn't often encountered, some websites confuse it with other species. However, the University of Texas provides a special page comparing Mimosa borealis to closely related species. That page is at http://www.biosci.utexas.edu/prc/digflora/mimosa/mimosa-dif.html.