Tag: senna

Seed of the Week: Desert Senna

Our wrinkly mystery seeds from last week were from desert senna, Senna covesii.


Often it is the desert senna’s bright yellow flowers that catch your eye, standing out against the gray-green foliage.


You might also “hear” the flowers because the bees that are attracted to them buzz pollinate, hanging onto the anthers and making a loud buzzing noise to vibrate the pollen loose.


You can even hear the plant when there aren’t any bees. As my friend Lynne points out, “You usually hear it before you see it. It can be in a non-blooming stage and you won’t notice it but you hear it rattle.” That characteristic has led to common names such as rattleweed or rattlebox.


The sound is produced by the loose seeds rattling in the seed pods. Eventually the pods split open, releasing the seeds. The open pods stay on the plant for some time.

Desert senna is native to the Southwest, so it doesn’t require much water. It is a low-growing perennial, reaching about two feet tall.

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In addition being attractive to bees, desert senna is also a host plant of the cloudless sulphur butterfly. It would make a wonderful addition to butterfly gardens.


Thank you to Lynne for all her help and contributions to this post.

Seed of the Week: Silver or Feathery Senna

Last week we experienced one of those times where the routine was destroyed. I apologize to those of you who were waiting to find out what the mystery seeds were. So, without further delay:

The mystery seeds were from the silver or feathery senna, Senna artemisioides.

You might know it under another name. It used to belong to the genus Cassia and so it often goes by its old names, silver of feathery cassia.


The silver or feathery part of the name comes from the silvery, lacy leaves.


Sennas are endemic to arid regions of Australia (Australian Native Plant Society), but they are used as landscape plants around the world.


Silver sennas are some of the first plants to bloom in the spring here in the Southwestern United States. They have cheerful bright yellow blossoms and a distinctive odor.


 Looking closely at the flowers, it becomes apparent that they have an unusual structure. The female part of the flower (carpel) is the light green part that curves off to the side from the center of the flower.


 The bottom flower in this photograph has lost the stamens (brown structures that are the male part of the flower), so you can see the hooked, bean-like female structure clearly.

Flowers with an asymmetric structure like this are somewhat unusual and it has to do with how they are pollinated. In Australia they are buzz pollinated, which means that bees clasp onto the stamens and vibrate them by buzzing to release the pollen. The female part stays off to the side and away from the action so to speak.


The female parts eventually mature into these pods that contain rows of black seeds.

In our yard at least, the seeds germinate readily and we could soon have a sea of sennas if we didn’t regularly weed them out.

Do sennas grow where you live?

Have you ever looked closely at the flowers?