Malacothamnus vs. Sphaeralcea

There usually is no issue in telling Malacothamnus and Sphaeralcea apart as Malacothamnus mostly grow outside of the desert and Sphaeralcea grow in the desert. There are however some Malacothamnus that grow in desert transition areas and sometimes grow with Sphaeralcea.

The first thing to look for is flower color, assuming there are flowers. Malacothamnus flowers are never orange. If the flowers are white to pink though, they could be a Sphaeralcea.

If the flowers aren't orange, it's very important to take photos of a side view of the calyx and bracts, stem, leaves, and more. Examples here:
https://www.inaturalist.org/projects/bush-mallows-the-genus-malacothamnus/journal/7179-photographing-bush-mallows-for-identification

To really confirm if you have a Malacothamnus vs. a Sphaeralcea when there is a question, you need to look at the fruit. Below shows the fruit of a Malacothamnus. The whole fruit is called a schizocarp which breaks apart into carpels. In Malacothamnus, the carpels completely separate into two halves.

Below is a comparison of Malacothamnus and Sphaeralcea carpels. The Malacothamnus carpels completely split into to two pieces. The Sphaeralcea carpels only partially open. Also note the net-like pattern on part of the Sphaeralcea carpel. This is sometimes obscure, but Sphaeralcea has this and Malacothamnus does not.

There are currently only four species of Malacothamnus that are known to occur with or near Sphaeralcea. M. densiflorus can be easily distinguished from Sphaeralcea where they grow together based on their longer and sparser hairs. The remainder aren't as obvious and I don't have time to go into detail at the moment, but still usually look different and comparing photos can help. See: M. orbiculatus, M. enigmaticus, and M. fasciculatus. The Sphaeralcea most commonly confused with Malacothamnus is S. ambigua var. rosea.

Posted on January 11, 2020 09:02 PM by keirmorse