Petalidium welwitschii

A harbinger of the Kaokoveld. Find Petalidium welwitschii, find the true Kaoko. You’ll first need to make your way through the Hartmann Mtns and Marienflüss. To our knowledge, this species is endemic to this very small stretch of Earth. In the second photo, bask in the weirdness of these two faces of P. welwitschii. These two branches actually derived from the same individual. And admire the Kunene River, across from which is Angola.

Wild collected, Namibia, Tripp & Dexter #4085 (RSA-POM); Photos by Erin Tripp

Petalidium variabile

This species is an absolute mess. It is WILDLY variable and likely forms hybrid swarms with who knows how many other species of Petalidium–and I think takes pride in such. Clearly, Petalidium variabile holds many evolutionary secrets that a botanist will want to soon unlock.

In the photos you can see two of the many faces that Petalidium variabile assumes. Also a nice field of it. (Is Kyle looking for plants or for chameleons?)

Oh – and Petalidium variabile is everywhere. And everywhere, it is…..variable. I guess the rest of us could learn a thing or two about plasticity.

Wild collected, Namibia, Tripp et al. #836, 873, 874, 1971 (RSA-POM); Photo by Erin Tripp

Wild collected, Namibia, Tripp & Dexter #4107 (RSA-POM); Photo by Erin Tripp

Petalidium subcrispum

You are looking at one of the most special plants in the world–really–lucky you to have stumbled upon this page! Here it is, Petalidium subcrispum, locally dominant and covering the bases of the Hartmann Mountains that flank the western margin of Marienflüss (looking north, the Angolan border is a mere 10 miles away).

But it grows nowhere else. That’s it: a local endemic, and as endemic as it gets.

We aren’t talking about subtle differences in morphology, here. This is a bona fide GOOD species: it isn’t confusable for anything else on Earth. Its floral syndrome suggests bee or other insect pollination. Purple flowered.

But here is the best part: its sister species, Petalidium subcrispum (red flowered, bird pollinated), grows abundantly just a couple of miles away — across the valley (Marienflüss), and flowers at the exact same time. Does pollen travel that far? Do the insects or birds that carry said pollen travel that far? If so, what maintains species boundaries? Kyle and I have been to the amazing Marienflüss three times now and have never seen a hybrid. This is a perfect in situ experiment for an eager graduate student who wants to escape to one of the more remote corners of the world. Maybe I’ll go back to grad school…..

Wild collected, Namibia, Tripp et al. #2013 (RSA-POM); Photo by Erin Tripp

Petalidium sp. nov–halimoides x setosum

On a special day towards the end of our May 2014 field trip, Essie, Leevi, Iain and I collected what appeared to be a Petalidium completely intermediate between P. setosum and P. halimoides. I’ve never seen anything like it.

A few intriguing observations: (1) it was growing vigorously and happily in a couple of minor, sandy drainages, but seen nowhere else along the way; I would have readily called it P. setosum, but (2) its leaves were glabrous instead of scabrous; (3) its inflorescences were nothing like typical P. setosum (lax, with wide bracts and bracteoles), but rather resembled perfectly those of P. halimoides (extremely congested with linear bracts and bracteoles); and (4) these plants were growing quite out of range for P. setosum. Like P. setosum, the plants did produce a musky honeysuckle floral smell typical of the former species.

Needless to say, I am very much looking forward to researching this, as soon as I have internet connection (the first time I’ve wanted it since our field trip began, to be sure!). It is mostly likely a naturally occurring hybrid, and one that needs a name….

Wild collected, Namibia, Klaassen et al. (awaiting data from Essie [WIND, COLO]); Photos by E. Tripp

Petalidium setosum

If you are a Latinist, you have already appreciated the specific epithet for what it means. The dense trichomes that cover the inflorescence bracts give this species its name.

Petalidium setosum is a highly distinctive, scandent shrub that is somewhat ‘special’ among Namibian Petalidium because of its large-ish geographical range… from north central Namibia to extreme southern portions of the country. But wherever it grows, you almost always find it in shallow depressions, indicating it is likely on the needier side of water availability. Its scabrous leaves and its lanceolate (not linear) inflorescence bracts (these densely covered by long, villous trichomes) make this species completely unmistakable.

That is, until you find a hybrid. That’s precisely what we think we found on our May 2014 outing (Essie Klaassen, Iain Darbyshire, Leevi Nanyeni, & Co.) in the Kaokoveld: a population of plants perfectly intermediate between Petalidium setosum and P. halimoides. It had the leaves of the former but lacked their scabrousness. It also had flowers that produced a musky odor, just like those of P. setosum. Yet, these plants had inflorescences of the latter—much denser and with linear bracts. Stay tuned for further study…. never a dull, unless it’s scabrous.

Wild collected, Namibia, Tripp & Dexter #887 (RSA-POM) [and numerous other times]; Photo by Erin Tripp

Petalidium rossmanianum

Holy smokes – what to do with this one? You look like, too much like, Petalidium variabile. But I want to believe you are distinguishable from that species for multiple reasons.

The identity crisis (which could be as much my problem as its) remains a mystery. We have encountered strange populations that seem to intergrade between ‘good’ P. rossmannianum and plants of the Petalidium variabile sort. We have encountered other populations where the differences seem so clear. Desperately awaiting molecular data.

Wish us luck. Kyle and I need it. Even Lucinda spent several puzzled moments by this ‘boot-if-ful’ species…

Wild collected [numerous times], Namibia, Tripp & Dexter #4053 (RSA); Photos by Erin Tripp

Petalidium rautanenii

A quick flash of something brilliant and summoning at 80 km / hr from the Land Cruiser. So alluring that even my mom noticed it (yep – fieldwork with the parents in Namibia – never a dull). We were gliding down a dirt highway not far from Waterberg when I first laid eyes on Petalidium rautanenii. 

Petalidium rautanenii cannot possibly confused with any other species in the genus, based on macromorphology alone. One of the very few taxa with gaudy, pure white flowers. I suspect my immediate love for it was far greater than its’ for me. Another unrequited…sigh.

This is my 23rd species (not including all the putative new species), and the most recent, that I have encountered in the field. It’s getting harder to find new ones without going to Angola, but, that being said, the world of discovery about each of those 23 is wide open. Community assembly, niche biology, adaptation, speciation, climate change tracking…. you name it.

Wild collected, Namibia, E. Tripp w/ L. Tripp & C. Tripp #4796 (COLO); Photos by Erin Tripp

Petalidium ramulosum

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You there! WHAT do you make of this? So clearly related to the ‘dense heads’ clade (not that we have much understanding of the phylogeny of Petalidium…. yet), but with heads much more lax than those of its close relatives, which we presume to be: P. setosum, P. lanatum, P. halimoides, P. canescens, and perhaps P. angustitibum (among other Angolan delicacies).

Petalidium ramulosum is absolutely distinctive within the genus by its low, creeping habit (check out those adventitious roots…don’t be jealous!). Although one can find this species on a few ‘roadsides’ in Namibia (roadsides in quotes because most Namibian roadsides are nearly as pristine as the rest of the landscape), you’ll be lucky if you do. It rarely exceeds 10 cm in height and spends its days buried far underneath the dense grasses. You would seek shelter from the scorching Namibian sun, too…

Moral of story: don’t settle for being an underdog. Look up to this species, which hasn’t let its short stature or unemphatic, low-profile give it a complex…Oh no. She creeps proudly!

Like any good Petalidium, this species has a rather restricted / limited distribution, worldwide. I don’t know how Kyle and I were so lucky to have found it. Its inflorescences remind me most of those of Petalidium angustitibum (check out photos of that species on this website), and I’d not be surprised if the two were each others closest relatives. Lucky them.

Wild collected, Namibia, Tripp & Dexter #4120 (RSA); Photos by Erin Tripp.

Petalidium pilosi-bracteolata

YOU are a problem child! Locally abundant (indeed dominant) in the greater Erongo region. But with a complex identity (derived from P. variabile? or not?)….sometimes with awesome, fimbriate trichomes. But not always. If you had them, you would only wear them on special occasions, too.

Wild collected, Namibia, Tripp & Dexter #876 and #4096 (RSA-POM); Photos by Erin Tripp

Petalidium physaloides


Everybody needs a compliment. For this plant, it is a stretch. Give me some flowers or at LEAST some fruits to work with.

We collected this as yet enigmatic plant in the depths of Van Zyl’s Pass… on the only day in my life that I have ever seen Kyle visibly nervous (yep, right before we decided that our Toyota could travel no further and, despite what all of the guidebooks say–that you cannot turn around in the middle of Van Zyl’s Pass once you initiate the traverse–Kyle and I used good judgement [for once] and spent the rest of the afternoon reconstructing the rocks that comprised the 4×4 track, by hand, and eventually made it out of the pass with success). This plant remains a huge mystery to us, but for now, we are calling it Petalidium physaloides. We aim to one day return to Van Zyl’s, more properly equipped, to figure this one out.

Wild collected, Namibia, Tripp & Dexter #844 (RSA-POM); Photo by Erin Tripp