|A structure called the rentinacula is a modified funiculus that acts like a catapult to launch mature seeds away from the parent plant. This structure is unique and shared among all Acanthaceae in the strict sense.|
|Namibia Field Work, 17 March - 3 April by Erin Tripp|
17 March 2010At present, I'm listening to Swedish National Public Radio over the satellite TV, doing DNA alignments, and waiting in my hotel room for the sun to rise (I made the mistake of thinking about coffee, which I hauled from the US, when I awoke at 03:00 under the influence of heavy jetlag). After 35 hours in transit, only 21 of which were in air, I reached Windhoek, Namibia late last night. I am here to collect species of Acanthaceae, as part of a recently launched NSF project on the systematics and evolution of the Ruellieae lineage. Specifically, I am drawn here by one plant group that has undergone a spectacular radiation contained almost wholly within the borders of Namibia: the genus Petalidium. In the field, we will attempt to find and study as many of the ca. 30 species of Petalidium as possible; I am also targeting the genus Ruelliopsis, Ruellia, and several other genera in Acanthaceae. The eventual goal is a worldwide synthesis of evolutionary relationships and diversification in Ruellieae, with relevant taxonomic revisions where necessary.
Today I will visit the WIND Herbarium at the National Botanical Research Institute to make contact with the local botanists and then go retrieve the research permit from the Ministry of the Environment and Tourism office. This evening I will be joined by my colleague Dr. Kyle Dexter, based at CNRS (Centre National de la Recherche Scientifique) in Toulouse, France. Given his research interests and experience, Kyle is sure to provide an interesting ecological evolutionary perspective on the Petalidium we will collect. Tomorrow morning we will go fetch the camping-equipped 4x4 that we rented for the work, then shop for food, a drum of water, fuel, and away we go.
19 MarchKyle and I haven't even been in the field 24 hours, and already we have found and collected three species of Petalidium (including P. rautanenii, P. englerianum, and one as yet unidentified), two Monechma, two Barleria, one Blepharis, and Megalochlamys. Two of the species of Petalidium were growing side by side, i.e., in "sympatry." We have also seen baboons, warthogs, kudu, a shaft-tailed wyndah, a plain-backed sunbird, and several common African grey hornbills. Despite being in one of the driest countries on Earth (indeed the driest in the Southern Hemisphere), we got caught in an awesome, torrential downpour just south of Otjiwarongo while trying to pitch camp last night. So we put the pitching on hold and seized the opportunity to bathe.
Today we are en route to Grootfontein to collect previously documented Acanth populations we have learned of via visits to various herbaria worldwide. This area hosts one of the world's richest deposits of a diversity of minerals, and is also site of the largest meteor to have struck the planet: the Hoba. We are lucky to drive under a ceiling of thick grey clouds. It looks a bit like California here (everything is transiently green) that there are next to no people and almost all the roads are sans pavement. Often we are the only ones on the road, which is a good thing given that both of us struggle with driving on the left-hand side. Occasional, extraneous honking sets one into paranoia that she is on the right (wrong) side again.
It is Namibian Independence Day and again, delightfully cloudy. We spent the morning pressing plants that we collected in the Grootfontein area, including the monotypic, regionally endemic, grass double "Ruelliopsis"(pic 2) that I was keen on finding, several Hypoestes, the miniature-flowered Blepharis maderaspatensis, and the first two species of Old World Ruellia I have ever seen “in the celluose”: R. otavensis and R. patula. We were joined by a local man, Petras Ambrosias, who walked up to inspect our activities with curiosity.We spent the morning together and taught him about our research activities, what we were doing, and why biodiversity is important to us. He learned quickly, and helped us press plants for the duration.
It has been a 24-hour Acanth fest. Yesterday, we passed thru Etosha National Park for some nice game and bird watching, en route to Kaokoland (northwestern Namibia). On the other side, west of Kamanjab, we were surprised by an unexpected landscape of large sedimentary mesas whose slopes were provisioned abundantly with Petalidium, a golden sunset, and a high elevation pass perfect for camping. These are the Grootberg Mountains near the Hoas Conservancy. There are a number of new Blepharis and Barleria here, too, including the orange sherbet-flowered Barleria senensis. The highlight was discovering that Acanths, as it turns out, are 100% capable of produceing flora aromas in the Old World (the family is generally considered to be odorless). One magnificent yellow-flowered and yellow-bracted, Petalidium giessii, smelled strongly of sweet jasmine. Nearby was the closely related Petalidium luteo-album, similar but with larger flowers and different bract and inflorescence morphology.
The next morning, we proceeded to find four additional species of Petalidium including one with white flowers and magenta and yellow stripes in the throat (Petalidium rossmanianum). We also collected a lovely Ecbolium (E. clarkei) before stopping to pitch camp and press plants just south of Opuwo, which in the Herero and Himba languages means "The End". In the Kunene political region, at the junction between the physiogeographic Kaokoland and Damaraland, Petalidium halimoides is eaten by rhinos and other game, and a decoction from its roots is drank by humans for stomach pains. Its name in Damara is !nahais (with the ! representing one of the four lingual clicks). In addition to this species, many other Petalidium are major food sources for grazing goats, cows, and wild game.
Our Toyota Hilux is fully equipped for camping, complete with a tent mounted to the top, a compressor for tires, a second car battery to power the cooler for cold camp beer, cheese, and vegetables, a propane stove for cooking, folding chairs and a table, and, although the dust does a fine job keeping hair grease in check, a giant water tank for much welcomed daily showering.
Two days ago, we set out for the hot, mountainous, and roadless Kaokoland, home to the Himba and Herero people and the greatest diversity of Petalidium on Earth. There are only 4 x 4 tracks, a GPS with plenty batteries, and good note-taking to navigate one's way to Kaoko's most northwesterly reaches: the desert Hartmann Mountains and the verdant Marienflüss to their east. This was our destination. We made it only halfway. As we came to learn, it was too great a risk coming here with only one vehicle (trucks almost always travel in caravans in the event of a breakdown), with only one spare, and with only mediocre ground clearance. Prior to departure, we were relying on seeing other safari trucks pass on occasion… but nothing. The safari season starts in April, and it was clear we were the first truck out in 2010. After a 200 km approach, we reached the treacherous 13 km long Van Zyl's Pass, which is said to be traversable only from east to west. We successfully completed its first few obstacles, but got hung up on a steep, rocky descent boasting a drop too great for our clearance. Our options were to try it with the awful and likely possibility of busting the radiator (thus having to abandon the truck and hike a great distance out), or attempt the reverse: Van Zyl's from west to east. We opted for the latter. It was the wise choice. After a few hours of manual modifications of the "road" (shuffling rocks around to facilitate our exit), we began our slow easterly retreat, with mixed feelings of relief and defeat.
But the good news is twofold. First, we now know how to attempt it next time: go with a caravan, higher ground clearance, a high-lift jack, and two spares. Second, we weren't out much botanically: we learned upon arrival that Kaoko has been extremely dry this year compared to other parts of Namibia and very little was in flower. While stuck in the gut of the pass, we did manage to collect two different species of Petalidium (the regional endemics P. ohopohense and P. physaloides) and a couple of other Acanths including an interesting Barleria (B. rogersii).
Today we retreated southward towards Sesfontein then took a 100 km northwest detour towards Purros. Staring out across a series of scorched, slaty, and soil-less mountain slopes, we expected to find little acanthaceous but were once again met with wonderful Namibian surprises. We found both the large red-flowered Ruellia diversifolia (pic 2) and the large red-flowered Petalidium coccineum in full halation. They were high on my “to see” list. We also found a mysterious ruellioid with large white and purple-striped flowers and an extremely unusual-shaped lower corolla lip. It will most likely turn out to be an undescribed species of Ruellia, sympatric with, vegetatively similar to, but otherwise markedly distinct from R. diversifolia. Fascinating. Genetic variation might well be the stuff of evolution, but morphological variation is the stuff of selection, at least by botanists. The following morning we conducted and filmed pollinator observations. The curve-billed Dusky Sunbird was the most frequent visitor to the red Ruellia and also to a second species of Petalidium we found later that day, P. variabile. [Perching sunbirds are, in a way, the Old World ecological counterpart to hovering New World hummingbirds].
We also collected population-level samples of Petalidium variabile (pic 2) with the hope of developing appropriate molecular markers for the genus in the future. Because we are probably witnessing "speciation in progress" in Petalidium, traditional molecular markers in plant systematics (i.e., species-level and above species-level markers) will likely provide insufficient data to attempt understand taxon delimitation, gene flow among populations, and ultimately, barriers to (or the lack of barriers to) reproductive isolation among populations. That is, population-level markers will be needed in this system.
Our workdays have been long, and sleep has been short, but we have been fortunate to find ourselves beneath some magnificent sunsets and have enjoyed several dry, breezy evening runs across uninhabited dirt roads underneath all that color. Plant pressing, which commences immediately following dinner, generally lasts well after midnight because we are pressing many replicate specimens for other institutions and are also collecting various tissue samples along with relevant data for further lab study. Given the black skies, bright Southern Cross, and most terrific Acanths, the long nights are tolerated effortlessly.
In the majority of habitats containing Petalidium here, there are literally thousands of individuals. They as well as other Acanths, namely Barleria and the well-armored Blepharis, are very often the dominant plants characterizing the landscape: the manzanitas of Namibia. They literally blanket the hillsides. This contrasts sharply with most New World habitats, which frequently contain Acanths but not in such great abundance. Further, sympatry of congeneric species is not at all uncommon here. One additional difference from New World plants seems to be nectar production and concentration. Almost all flowers that we attempted to pipette nectar from lacked it; those that contained nectar had very high sugar ratios. For example, hummingbird pollinated plants in the neotropics typically have dilute (but copious) nectar, with percent sucrose averaging in the low 20s. Here, bird-pollinated flowers such as those of Ruellia diversifolia typically contain nectar with > 30% sucrose. This could be due to greater evaporation… different ecological strategies… chance / sampling error… all hypotheses yet to be tested.
Two days ago, we departed Kunene Province southbound towards the next set of localities in Damaraland. On our way, we spotted a rare desert elephant and, perhaps more notably, its enormous, grass-scented feces (the grass diversity, afterall, is impressive here: you can't blame him). The sheer bleakness of a thousand square kilometers of near lifeless dunes and relentless sandstorms beckoned our alternative route choice through the Skeleton Coast Park towards Brandberg Mountain. We found another species of Petalidium (one with endearing, miniature brick-red flowers: P. lanatum) and Blepharis (B. grossa) along the way, growing among the Welwitschia just east of the Park entrance. In the Park, we saw shipwrecks and saltroads and lichens clinging a bewildering diversity of rocks, but little else.
We completed our field collections for the trip over the course of the last three days because we needed time to return to the herbarium to dry plants and identify our specimens with the good reference collection at WIND. Our first stop was the foothills of the Brandberg Mountains, famous not (yet) because of their Acanths but because of the mysterious White Lady rock painting, dated to ca. 16,000 ypb, and said to have been the product of the first observance of fair skin by the ancestral Damara group here. We collected several different species of Acanthaceae, including the striking Petalidium canescens with its inflorescence heads achieving the size of softballs and consisting of perhaps hundreds of fruits (=very unusual in Acanthaceae). We also collected a Ruellia (in fruit only, precluding its identification) whose leaves smelled exceptionally of citronella.
When collecting plants car-style, I generally stop to dry them in hotel rooms overnight with a brought along space heater. The thermometer near the Brandberg trailhead registered 47°C (116°F). As such, our combined approach of strapping plants to the top of the car while driving mixed with removing and piling hot rocks among small stacks of them (“the spa treatment”) cooked them up just right. After Brandberg, we passed through the Erongo Mountains to collect, and then made a slow retreat back to Windhoek via one of three passes that cuts through the beautiful Khomas Hochland mountain range. We took the northern route through the steep and scenic Bosua Pass, where we happened upon the 14th (and our final) species of Petalidium on this trip (the attractive P. setosum), which smelled of musky honeysuckle and was visited abundantly by honeybees. This species is morphologically interesting because its style is held in a "rugula" (a groove of sorts in the upper corolla lip), which in general characterizes many species in the Justicieae, not Ruellieae, lineage.
Back in Windhoek, Kyle and I sorted plants, got them into the driers for the final dessication, and worked on identifying our collections in the herbarium for two days. In total, we made over a hundred Acanth collections (most of them of different species) in duplicates of six or seven so that specimens can be distributed to natural history museums worldwide (i.e., in addition to Rancho Santa Ana Botanic Garden and NBRI in Windhoek, specimens will be shipped to Missouri Botanic Garden, The United States National Herbarium / Smithsonian, The New York Botanical Garden, California Academy of Sciences, and The Royal Botanic Gardens, Kew). Kyle has been a tremendous help and I couldn't have asked for a better “field assistant” as well as traveling companion.
We corresponded with Ezekiel Kwembeya (the head curator), Esmerialda Klassen (a botanical researcher), and other herbarium staff, and thanked them for their very kind assistance. The staff and facility here are most welcoming and indeed Namibia has been a terrific place to work. I am in communication with Ezekiel and a student / herbarium technician here, Hendrina Hasheela, about the prospects of getting started on a treatment of Acanthaceae for Namibia. Hendrina is interested in the family and would like to work with me on the project, and because the Acanthaceae among the most dominant and diverse plant families in Namibia, Ezekiel is keen on getting that house in order. If and when grant funds are procured, the intention is to return to Namibian for additional field trips and bring Hendrina along for the work. The present trip was a short but productive one. Importantly, it was also insightful in terms of what to do differently next time.
The herbarium closed for Good Friday, and because Kyle and I had to return presses and have all our plants in the driers before quitting time Thursday evening, we wound up with a day of vacation. So like the majority of other tourists to Namibia, we punched it down to Sesreim and Sossusvlei to see, at 300 m, the tallest sand dunes in the world (Namib-Naukluft Park). Unlike the majority of other tourists to Namibia, we were still looking for Acanthaceae, and saw at least six different species (that we hadn’t yet collected) along the way. We camped just outside the Park the night before the dunes, under another phenomenally black starry sky, this one punctured by an uninterrupted three-hour heat lightning episode. The next morning, we drove the additional 80 km to the dunes. The shadows cast by their curves across such smooth and uniform surfaces is an image like no other. We enjoyed a couple of blistering hot, barefoot hikes up their ridges before our return drive to Windhoek via the western outskirts of the vast, flat Kalahari Desert.
The geology has been most impressive on this trip (as have been the overall litter-free roads and friendliness of the people). My working hypothesis is that such diverse geological substrates, from volcanic rocks to dolorite, sandstones, slate, and red clay have combined with a mountainous terrain to help facilitate speciation in Petalidium — a hypothesis to be tested. At present, I am en route to Addis Ababa, Ethiopia, for the second half of the Africa collecting trip. There, I am to meet up with Dr. Ensermu Kelbessa, Curator at the National Herbarium, Professor at Addis Ababa University, and Acanthaceae specialist. He will join me for fieldwork near the Kenyan, Somalian, and Sudanese borders. Ethiopia is going to be very different. Time to celebrate diversity.
We saw a lot of animals, on the trip the birds, particularly the ostriches and the black-winged stilt, were my favorites; the nocturnal bat-eared fox, with its peculiar rooting around the ground for termites, topped my mammal list. Those that we bothered to identify are listed below.
Hartmann’s mountain zebra
South African ground squirrel
various small rat-like things
African grey hornbill
South African shelduck
Shikra (little banded goshawk)
Northern black korhaan
Cape turtle dove
Grey go-away bird (lourie)
Southern yellow-billed hornbill
Acacia pied barbet