This is a DAMN fine species and you would be hard pressed to ever find anything so beautiful in the Logee’s catalogue. Petalidium luteo-album is clearly the sister species to P. giessii. It (P. luteo-album) also occurs with the latter (P. giessii) in the Grootberg Mountains (= geological capital of the universe), but also has a much wider range, extending into the northern Kaokoveld. It is also the only species of Petalidium that produces truly succulent leaves.
In May 2014, we found our first ever mixed population of the two species (P. luteo-album and P. giessii). How on Earth do these species maintain reproductive isolation? They were flowering concurrently, and literally doing so side-by-side (see photo of the two, laid against a herbarium blotter). In all fairness, it did seem that the former was going out of flower just as the latter was coming into flower, which is precisely what one would expect under reproductive character displacement scenarios. In any case, the population is georeferenced, and desperately in need of further field (and genetic) study.
Photo with the ruler so clearly shows the genus synapomorphy: paired bracts subtending each flower. That photo also very nicely shows the ribbed (‘herringbone’) patterning on the lower portion of the corolla throat. It doesn’t matter which way you twist the flower around, or whether you look at it while standing on your head. Petalidium luteo-album will forever enchant you. Watch out for the spell.
Wild collected, Namibia, Tripp & Dexter #830 (RSA-POM); Photo by Erin Tripp