Wednesday, May 8, 2013

Introduced Plants - circa 1723

Introduced species are a big deal in ecology. Species move around all the time, of course, but natural evolution tends to be slow and gradual. Plant species that evolve in a place are adapted to the local environment, and while the "balance of nature" is something of a myth, slow evolution makes for more stability. Introduced species appear abruptly, without slowly accommodating to the denizens already in place. Introductions may run roughshod over the local inhabitants because they aren't vulnerable to the general threats - these introduced species can become invasive. Humans have introduced species all over the world, both deliberately and accidentally. The process of introduction really took off in the 17th and 18th centuries, as Europeans sailed all over the globe and carried plant materials back with them.

But how can you tell if a species is introduced? How do you know when an introduction occurred?

Charleston, South Carolina, was founded in 1670. By 1690 it had become one of the five largest cities in the colonies. It was a major port and a hub of trade between the American colonies and the Atlantic. Ships arrived in Charleston from many locations. Ships arriving from Africa brought slaves. Ships from England and the rest of Europe brought settlers and manufactured goods. Ships from the Caribbean and South America would also have stopped in at Charleston.

Mark Catesby visited Carolina in the period between creation of the crown colony of Carolina in 1719 and the separation of South Carolina from North Carolina in 1729. He arrived fifty years after Charleston was established, and after decades of transit and trade had moved around myriad plants and animals, but BEFORE extensive European settlement of the area. The plants he collected thus contain a snapshot of the botany of the region early in the colonization process. Most of his collections are native species, but some introductions had already arrived.

The following species in Catesby's collections are all considered to be introduced or possibly introduced to the Carolinas (per Alan Weakley):
Dysphania ambrosioides (Linnaeus) Mosyakin & Clemants        00087426R
Gaillardia pulchella Fougeroux var. pulchella        00087294U, Sher-1957
Helianthus debilis Nuttall    Sher-1944-2
Stokesia laevis (Hill) Greene            Sher-1641
Tarenaya hassleriana (Chodat) H.H. Iltis = Cleome hassleriana Chodat            00087297X
Ipomoea coccinea L.  H.S. 232 f.61
Jacquemontia tamnifolia (Linnaeus) Grisebach    00087560Q, Sher-0359
Momordica charantia L.        Sher-2195
Croton glandulosus Linnaeus var. septentrionalis Müller of Aargau      Sher-2069
Indigofera tinctoria L.           H.S. 232 f.106
Mimosa quadrivalvis L.         H.S. 232 f.107
Senna occidentalis (L.) Link             H.S. 212 f.1, H.S. 212 f.81
Nepeta cataria L.       00087449W
Prunella vulgaris L.   00087454S
Modiola caroliniana (L.) G. Don       00087276U, Hort-004-004
Sida rhombifolia L.    00095695Y, H.S. 212 f.51, H.S. 212 f.50
Digitaria sanguinalis (L.) Scopoli     Sher-0125
Echinochloa crusgalli (L.) Palisot de Beauvois       00087523P
Eleusine indica (L.) Gaertn. H.S. 212 f.85, 00087562S
Eragrostis cilianensis (Allioni) Vignolo ex Janchen           00087570R
Hackelochloa granularis (L.) Kuntze           00087527T

NB: H.S. references are in the Sloane Herbarium. Sher-#### and 00##### references are in the herbaria at Oxford University.

Some introductions were likely deliberate. Nepeta cataria L. (00087449W) is catnip, a common garden herb native to Eurasia. It is easy to imagine a colonist bringing seeds from Europe to start an herb garden in Carolina.   

Tarenaya hassleriana (Chodat) H.H. Iltis (syn. Cleome hassleriana Chodat, 00087297X), is the spiderflower or spider plant commonly grown as an ornamental. The note on the bottom of the herbarium sheet reads “Sent from South Carolina by Mr. Mark Catesby.” This species is native to South America. The Flora of North America describes it thus: “Tarenaya hassleriana is native to Argentina, Brazil, and Paraguay. It is often cultivated and has sometimes escaped and naturalized. In cultivation and various floras, it has long been treated under the name Cleome spinosa…..”.  

Cleome was apparently a favorite of Thomas Jefferson, who grew it in his gardens at Monticello; construction on the house began in 1768 and work on house and gardens continued for several decades. The plant is an aggressive self-seeder.
So did Catesby really find this plant in South Carolina? It is plausible; certainly there had been traffic between the cleome’s native range and the Carolinas for decades by the time he visited.
The presence of particular taxa in Catesby’s collections may or may not be significant. It is impossible to know where he collected his specimens, or the conditions in which they were growing. He certainly could have gathered plants from cultivated gardens. But it is also possible that some of the introduced plants he collected had already escaped from cultivation. It is also true that we do not know for certain that the plants in the herbaria were collected in Carolina; even the ones with handwritten notes claiming South Carolina provenance might have in fact been collected elsewhere. What we can say, however, is that the presence of these taxa in Catesby’s collections strongly suggests that these plants were growing in South Carolina or possibly Georgia in the 1720s.