26 de julio de 2023

#3 Random ramblings about Asclepias

I recently started an instagram page (@bay_state_botanist) to document my learning about the flora of New England, with reference to my South African perspective where there is any connection or relevance.

After seeing my first individuals of the striking Asclepias tuberosa on Martha's Vineyard last weekend, I was reminded of the few Asclepiad species I've seen in Cape Town, specifically A. crispa and Gomphocarpus physocarpus. Here is what I wrote:

"The striking orange flowers of the butterfly weed, Asclepias tuberosa, one of the more common milkweed (Apocynaceae) species of eastern and south western North America. These ones I saw between Edgartown and Oak Bluffs on Martha's Vineyard were being pollinated by a variety of beetles, flies and bees.

Milkweeds are usually known for their stems that contain milky saps which drip out when the stem is broken. This milkweed is an exception. Nevertheless it is still toxic to consume in large amounts, and like other American milkweeds, the leaves are an important food source for monarch butterfly caterpillars.

Native Americans have traditionally used milkweed roots as treatment for pleurisy (inflammation of tissues around the lungs and chest cavity) and other pulmonary issues. As far as I understand this is why the genus was named "Asclepias", after Asclepius who in Greek mythology was a mortal who eventually became the god of medicine. His rod, a staff with snakes wrapped around it, is still used in many medical symbols today. [I have more to say about this; the rod is sometimes that of Hermes/Mercury rather than Asclepius, but I won't get too sidetracked...]

There's an interesting connection between my two worlds of the US and SA regarding this genus. Asclepias are found in the Americas and in southern Africa. The 5th photo shows an Asclepias crispa I saw growing near Rhodes Memorial on Devil's Peak in Cape Town. Disjunct distributions of closely related species like these provide support for the continental drift theory. The idea is that at one time many millions of years ago these lands were connected, and the common ancestor of these two Asclepias species lived on that land. Since then they have speciated and adapted to their different environmental conditions.

The last two photos show the invasive Gomphocarpus physocarpus (balloon plant) growing in Kirstenhof wetlands in Cape Town. It's a species of milkweed that has spread across much of the world. You can see how similar its flowers are to the Asclepias. The main difference between the two genera is that Gomphocarpus has fibrous roots and woody branched stems while Asclepias has tuberous roots and annual, unbranched stems.

The milkweeds of North America are famous for being the food source of the monarch butterfly Danaus plexippus which migrates from Mexico to the US each year. Interestingly the southern African milkweeds also have their own African monarchs, Danaus chrysippus. Both butterfly species can ingest the milkweed toxins and store them in their bodies, making them distasteful to predators. The close genetic relationship and behavioral similarities of these two monarch species on different continents also suggests a once uniform land mass that since broke apart. In biogeography they would be called vicarious species.

Molecular work to better understand the genetic differences between Asclepias and Gomphocarpus is ongoing. My filed guide to the flora of Table Mountain from the early 2000s actually refers to Asclepias crispa as Gomphocarpus crispa, which confused me when I first started botanizing and led me to research this family a bit deeper in this post."

I've done a little more browsing of the scientific literature on Asclepiad biogeography and it seems my assumption about African-North American vicariance is not necessarily supported by the research.

Rapini et al. (2007) write that the Asclepiadoideae subfamily "colonized the New World at four different times, suggesting independent dispersals from the Old World rather than any kind of vicariant event. The clade with Metastelmatinae, Oxypetalinae, and Gonolobinae (MOG, see introduction) was the first to arrive, at 32 Ma; three other invasions were more recent, with Cynanchum at around 24 Ma, Asclepias 20 Ma, and Marsdenia 16 Ma. Between 32 and 16 Ma, South America was a continental island (Raven & Axelrod, 1974a, b). In contrast, North America was connected to eastern Asia through the Bering Strait, a route probably permeable for temperate taxa until the end of the Oligocene, but possibly later."

"The assumed Asian sister group of Asclepias, however, is hypothesized as extinct."

I guess this is still vicariance in a way, just not in the direction I had assumed.

Though I'm not a taxonomist or biogeographer, I find piecing together the evolutionary trajectory of taxa and trying to decipher the complex puzzle of patterns we see today, very interesting. If you are curious about the dispersal and diversification of the other Asclepiadoideae clades in the New World, I'd recommend reading Rapini et al. (2007). It's available through Lib Gen if you don't have an account with the publisher (DOI: http://dx.doi.org/10.3417/0026-6493(2007)94[407:DOAAIT]2.0.CO;2).

Fishbein et al. (2011): "Phylogenetic Relationships of Asclepias (Apocynaceae) Inferred from Non-coding Chloroplast DNA Sequences" is also a good read.

Other sources used for my IG post:

Thanks for reading if you made it this far.

Publicado el 26 de julio de 2023 15:28 por tim_kirsten tim_kirsten | 2 observaciones | 2 comentarios | Deja un comentario

9 de mayo de 2023

Tim rambles on #2

Today's post is about STAR OF THE SEA Reserve, managed by the Dartmouth National Resources Trust (DNRT) but which also crosses into town-owned land. I volunteered with DNRT a few weeks ago where I helped put up some nesting boxes for the Eastern blue bird (https://www.inaturalist.org/taxa/12942-Sialia-sialis) and learned to identify some of the main invasive plants in the area: garlic mustard, Japanese knotweed and multiflora rose.

I've visited the reserve three times, two during the day for some longer walks (1 and 8 May) and once in the evening to see the setting sun over the water (3 May). All three visits have been rewarding. The DNRT manages a large network of small reserves and it's inspiring seeing the results of their conservation efforts.

The reserve sits on the coast of southern Massachusetts along the Apponagansett Bay, which is itself a small inlet withing the greater Buzzards Bay. The land around it is claimed by some relatively large houses, given its proximity to the water. On its southern (coastal) edge of the reserve is a salt marsh habitat, home to mud fiddler crabs and wading birds and subject to large intertidal water level fluctuations.

Just north of that the habitat changes to deciduous woodland/wetland (blue trail on their map), and at this time of year much of the forest is flooded (post-winter snowmelt and spring rains make this the wettest season in New England). The difference between the extent of flooding on 1 May, after a weekend of rain, and 8 May (a sunny weekend) was clear; much of the water had retreated though some streams and large pools remained. This part of the reserve has many wildflowers, mostly wood anemone, violet spp., northern starflower, sessile bellwort, jack in the pulpit, marsh marigold, canada mayflower and dwarf ginseng. There are also lovely dense pockets of cinnamon fern, sensitive fern and some other fern species, as well as horsetails and fan clubmoss.

Further north of this (red trail on their map), the habitat changes slightly, though I am still trying to pinpoint all the exact differences. The elevation is marginally higher, with there being fewer wet areas, but not drastically so. The soil is possibly more acidic and sandy, as the dominant trees here are eastern white pines, and the soil is lighter in colour than the southern habitat. There are also almost no wildflowers here, as far as I have observed anyway. There also seems to be more light hitting the forest floor in this area, possibly because of the canopy features of pine. Fewer ferns too. And less deciduous leaf litter of course. The floristic transition therefore makes sense: light, water and nutrient availability all change quickly between the habitats

The DNRT describes the reserve like this: "DNRT’s Star of the Sea Reserve was extensively mined for sand and gravel and the old gravel pits, with all the top soil gone and excavated down to the water table in spots, is made up of grey birch, scrubby oaks and bayberry, the insectivorous sundew and cranberry growing in the poor soil conditions. In the eastern portion, rushes, orchids and Joe pye weed indicate some of the wetter areas, along with cacophonous groups of spring peepers."

Perhaps another key to the difference in habitats (besides elevation) is land use history- the northern parts maybe were not mined while the southern habitat was. Either way I find the subtle changes very interesting.

Another interesting observation I've been pondering is the total lack of skunk cabbage. I've seen this spring wetland species at every other wetland area in MA and Rhode Island I've visited or driven through over the last month. The large network of seasonal puddles in this reserve seems perfect habitat for skunk cabbage. Maybe it's been locally extirpated as a result of the sand mining? I'd appreciate any insight on this.

I've also yet to see the orchids and joe pye weed mentioned on the DNRT site but it may be too early for them.

Lastly, I unintentionally started an interesting discussion around the confusing taxonomy and identification of the white violets (https://www.inaturalist.org/observations/160609506). I noticed a population of these growing near the boardwalk in a wetland section and assumed it was the same white bog violet I'd seen in Warren RI, but now I've learned how important leaf characteristics are in IDing this big genus. I love that about iNat- it's a great way to improve my botanical skills.

Also saw a cute eastern garter snake (which looks a lot like the cape skinks I am used to seeing in my garden in Kirstenhof in SA) and two wood frogs, which is a lifer species for me.

Publicado el 9 de mayo de 2023 13:46 por tim_kirsten tim_kirsten | 49 observaciones | 2 comentarios | Deja un comentario

24 de abril de 2023

Tim's Naturalist blog - The Striar Conservancy, Halifax, MA, USA

Date: Sun 16 April 2023

Location: Striar Conservancy, owned by the Wildlands Trust, a conservation org operating in southern MA. 168 acres.

Trail description: 1.5 mile loop that passes 5 or 6 vernal pools, so visiting in Spring is a must. Also has a nice view (with a bench) of the Winnetuxet river, about halfway along the trail. I gasped when I saw the view, it's really nice seeing this open vista after being in the closed canopy of the forest, and it seemingly comes out of nowhere. The path crosses over some meandering small streams which are also really pretty and add variety to the trail.

After stopping at 4 or so vernal pools looking closely for herps I was ready to accept that the beautiful trail itself would just be the highlight and that I wouldn't see the Endangered spotted turtle which the sign board at the head of the trail mentioned to look out for. Then at the 5th pool I saw something on a log about 15 m into the large pool. I got my binocs and voila, three spotted turtles were there! I wasn't prepared for their striking orange necks and bright spots on the backs of the shells. I felt that sense of awe that reminds me why I love naturalising, that thrill when you see an exciting species you've been searching for or a threatened species you weren't. Or some new unexpected organism that just looks so cool you can't help but feel like excited. It was a magical moment that it inspired me to start writing some short notes on my iNat journal for walks I do, so that's what this is.

As soon as I moved to try get to a better angle for photographing (lots of hanging vines and thicket making it hard to focus my basic camera) the turtles disappeared into the water, showing how shy they were and making the observation all the more special.

There were also lots of small trees/ tall shrubs of Vaccinium, with light green leaves and ericoid white flowers. Vaccinium is an important genus in New England, as it includes the blueberries and cranberries we eat. It's also cool seeing another genus of the Ericaceae, which has experienced wild speciation in Southern Africa in the Erica genus (>600 spp.) - these are the Ericas I am most familiar with. Seeing its cousins here in a different climate zone and over a great distance, yet still having very similar flower morphology, is cool and gets me thinking about its biogeographic history.

Fav observations: Animal: spotted turtle (Clemmys guttata). https://www.inaturalist.org/observations/155354274
Plant: this unidentified Vaccinum (blueberry) that has got me trying to learn more about traits differentiating species of this genus. https://www.inaturalist.org/observations/155349949

Other notes: my first time observing Ilex glabra (gallberry). Various mayfly adult exoskeletons attached to leaves of various tree spp. Anemonoides quinquefolia (wood anemone) only spring wildflower blooming at multiple points along trail. Lots of flat clubmoss (Dendrolycopodium obscurum). Heard a hairy woodpecker call. Trail was relatively quiet - only encountered 2 or 3 other groups/couples walking.

Overall, 8/10 trail. Wish I'd had more time to explore the other paths leading off the main one. But a great way to see vernal pools and typical SE MA forest species. Not many wildflowers yet other than wood anemone.

Read more about the Striar conservancy: https://wildlandstrust.org/striar-conservancy

Publicado el 24 de abril de 2023 15:31 por tim_kirsten tim_kirsten | 9 observaciones | 0 comentarios | Deja un comentario