Botanical sightseeing: Torreya species in Florida and California

This past summer, I visited Florida’s Torreya State Park to see the United States’ rarest tree species. Located along the eastern bank of the Apalachicola River, this state park protects Torreya taxifolia, an endangered and extremely range-restricted gymnosperm species in the family Taxaceae (the yew family).

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Torreya species in the United States. A. Global range of Torreya californica. B. Global range of Torreya taxifolia. Maps not to scale. Images in public domain, from Little (1971) via Wikimedia Commons (https://commons.wikimedia.org/wiki/Category:Torreya).

My interest in Torreya began several years ago, when I was working in California doing fire ecology fieldwork. On one of our weekends off, my friend Paul and I decided to go hiking at Mt. Tamalpais, a 784-meter peak between San Francisco Bay and the Pacific Ocean. Being botanists, we planned our hike based on the plants we wanted to see; we acquired recent specimen data (including GPS points) from herbarium records, overlaid those points on the trail map, and picked a route accordingly.

One of the plants we were looking for was Torreya californica, a California-endemic species in a small (<10 species) northern hemisphere genus.* Torreya californica is locally abundant in ravine habitats throughout the California Coastal Ranges and Sierra Nevada. The beginning of our search was filled with false starts, as time after time we would catch sight of some distant tree which we were sure was the one we wanted, only to find that, upon a closer inspection, it was just another Douglas-fir (Pseudotsuga menziesii).

We finally spotted a grove of our trees of interest as we got closer to the top of the mountain.

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Torreya californica (habitus). Very different from Douglas-fir once you’ve actually seen both of them.
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Torreya californica (leaves). Those spine tips are sharp!
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Torreya californica (seed in aril). Sometimes called a “drupe” in older literature. But this is not a fruit… Torreya is a gymnosperm.

Fast-forward three years, and I was in Florida doing vegetation mapping fieldwork in Gulf Islands National Seashore. I decided that since I’d already seen one of the two Torreya species in the United States, I ought to see the other—Florida’s Torreya taxifolia.

Florida torreya was once an abundant species within its very limited distribution. Today is a different story: “Since 1962 there have been no observed canopy sized trees, nor mature seed producing trees” (Schwartz et al. 2000a). Over the last century, particularly since the 1950s, the population  of Torreya taxifolia has declined by around 98.5 percent due to disease and complicating environmental changes (Lee 1995Schwartz and Hermann 1999; Schwartz et al. 1995, 2000a; Smith et al. 2011).

When I arrived at the state park, I saw Torreya taxifolia almost immediately—planted near the parking lot.

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Saplings of  Torreya taxifolia. I visited on a rainy day, so all my pictures are, unfortunately, somewhat blurry.
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Torreya taxifolia leaves.

Nearby, I caught a glimpse of a larger tree. I’m not sure whether it was also planted or whether it is a naturally occurring individual.

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A larger individual of Torreya taxifolia. Note its position as a subcanopy tree.

I hiked a few of the park’s trails, but the rain (at one point I was caught in a downpour) prevented me from exploring the area as thoroughly as I would have liked. I looked closely for Torreya taxifolia whenever a trail intersected a ravine (the species’ preferred habitat), but didn’t see any live individuals aside from those at the entrance.

What does the future hold for Florida torreya? The species is likely to persist in the short term (Schwartz et al. 2000b), but in the long term, extinction in the wild is a real threat. There are currently in situ and ex situ conservation efforts to protect this species, and one group is advocating for assisted migration (http://www.torreyaguardians.org). I’m hopeful that some of these conservation projects will be successful; for now, I’m glad that I had the chance to see this species growing in its native range.

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* Extant Torreya species are present in the United States and eastern Asia; however, fossil evidence shows that the genus also occurred in Europe up to the Pleistocene (Li et al. 2001). See Burke (1975) and Jang et al. (2001) for additional information on the economic botany of this genus; see Xiao et al. (2008) and Ghimire and Heo (2014) to put this genus in a phylogenetic context.

 

Literature Cited

Burke, J. G. 1975. Human use of the California nutmeg tree, Torreya californica, and of other members of the genus. Economic Botany 29(2): 127-140.

Ghimire, B. and K. Heo. 2014. Cladistic analysis of Taxaceae sl. Plant systematics and evolution 300(2): 217-223.

Jang, Y. P., S. R. Kim, and Y. C. Kim. 2001. Neuroprotective dibenzylbutyrolactone lignans of Torreya nucifera. Planta medica 67(5): 470-472.

Lee, J. C., X. Yang, M. W. Schwartz, G. Strobel, and J. Clardy. 1995. The relationship between an endangered North American tree and an endophytic fungus. Chemistry & biology 2(11): 721-727.

Li, J., C. C. Davis, M. J. Donoghue, S. Kelley, and P. Del Tredici. 2001. Phylogenetic relationships of Torreya (Taxaceae) inferred from sequences of nuclear ribosomal DNA ITS region. Harvard Papers in Botany 6(1): 275-281.

Little, E.L., Jr. 1971. Atlas of United States trees, volume 1: Conifers and important hardwoods. U.S. Department of Agriculture Miscellaneous Publication 1146, 9 p., 200 maps.

Schwartz, M. W. and S. M. Hermann. 1999. Is slow growth of the endangered Torreya taxifolia (Arn.) normal? Journal of the Torrey Botanical Society 126(4): 307-312.

Schwartz, M. W., S. M. Hermann, and C. S. Vogel.  1995. The catastrophic loss of Torreya taxifolia: Assessing environmental induction of disease hypotheses. Ecological Applications 5(2): 501-516.

Schwartz, M. W., S. M. Hermann, and P. J. van Mantgem. 2000a. Estimating the magnitude of decline of the Florida torreya (Torreya taxifolia Arn.). Biological Conservation 95(1): 77-84.

Schwartz, M. W.,  S. M. Hermann, and P. J. van Mantgem. 2000b. Population persistence in Florida torreya: comparing modeled projections of a declining coniferous tree. Conservation Biology 14(4): 1023-1033.

Smith, J. A., K. O’Donnell, L. L. Mount, K. Shin, K. Peacock, A. Trulock, T. Spector, J. Cruse-Sanders, and R. Determann. 2011. A novel Fusarium species causes a canker disease of the critically endangered conifer, Torreya taxifolia. Plant Disease 95(6 (): 633-639.

Xiao, P. G., B. Huang, G. B. Ge, and L. Yang. 2008. Interspecific relationships and origins of Taxaceae and Cephalotaxaceae revealed by partitioned Bayesian analyses of chloroplast and nuclear DNA sequences. Plant Systematics and Evolution 276(1-2): 89-104.

 

Soil-dwelling lichens of Gulf Islands National Seashore

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Vegetation in Gulf Islands National Seashore dominated by soil-dwelling lichens, mostly Cladonia leporina. Graminoids and dwarf shrubs are also present. This picture was taken near the edge of a sandy upland area; the middle of this area had less lichen cover and more species of herbaceous vascular plants.

This summer I am—officially—conducting vegetation surveys of vascular plants. But while I do love the beauty and diversity of tracheophytes, I am a cryptogam biologist at heart. When our team was in Big Thicket National Preserve earlier this summer, I identified (with Reese 1984 and other sources) any moss or liverwort species that covered at least 1% of a survey plot. In Big Thicket, wet floodplains whose non-woody vegetation is dominated by Sphagnum palustre and Pallavicinia lyellii occur frequently throughout the park. Drier upland sites sometimes support Leucobryum glaucum and Atrichum angustatum, although these species are never dominant.

Now we are working at Gulf Islands National Seashore, and the bryoflora is much less conspicuous. Aside from one wet depression in the middle of Quercus geminata shrubland, which at ground level was covered by a Sphagnum sp. I have yet to identify, I have not seen any sites where bryophytes form a dominant component of the vegetation.

But while Gulf Islands hasn’t been a bryologist’s paradise, I have been pleasantly surprised by the prominent role terricolous (soil-dwelling) lichens play in some of the park’s habitats. Three species of Cladonia are of particular note: C. leporina, C. prostrata, and C. evansii. They all seem to be most abundant in the Naval Live Oaks and Fort Pickens areas of the park, although I have seen them, albeit not in any abundance, in other areas.

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Cladonia leporina. This species is unique among “red-fruited” Cladonia in having richly-branched podetia (Hammer 2001).

These three species are all characteristic of the southeast coastal plain and are found growing on sandy soils in full or partial sunlight. Cladonia prostrata has the most restricted range; it is found in Florida and adjoining states. Cladonia evansii can be seen further north along the Atlantic coast, while C. leporina has the broadest range of the three and occurs in more inland areas towards the southern Appalachians (Brodo et al. 2001).

In our field sites, I have seen Cladonia evansii most often in semi-shaded areas under an oak canopy. Cladonia prostrata and C. leporina have seemed more common at more exposed sites, either under a sparse layer of shrubby oaks or in gaps in herbaceous vegetation. Vegetation communities containing Cladonia species have tended to be in areas of stable soil: relic dunes and sandy uplands.

Cladonia species have received some attention in ecological studies of Florida scrubland. They may suppress seedling recruitment in vascular plants (Hawkes and Menges 2003). In addition, they tend to become more abundant in post-fire landscapes (Menges and Kohfeldt 1995) and benefit from larger gaps in shrub vegetation (Menges et al. 2008).

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Cladonia prostrata. This species is sometimes called “resurrection Cladonia” because its large squamules noticeably curl up when dry and unfurl when wet.

 

UPDATE, 30 AUGUST 2016: When I originally wrote this post, I hadn’t taken any photos of Cladonia evansii. Below are a couple from today’s fieldwork.

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Literature Cited

Brodo, I. M., S. D. Sharnoff, and S. Sharnoff. 2001. Lichens of North America. Yale University Press, New Haven, CT, USA.

Hammer, S. 2001. Growth dynamics and the taxonomic status of Cladonia leporina. Rhodora 103(916): 405-415.

Hawkes, C. V. and E. S. Menges. 2003. Effects of lichens on seedling emergence in a xeric Florida shrubland. Southeastern Naturalist 2(2), 223–234.

Menges, E. S. and N. Kohfeldt. 1995. Life history strategies of Florida scrub plants in relation to fire. Bulletin of the Torrey Botanical Club 122(4): 282–297.

Menges, E. S., A. Craddock, J. Salo, R. Zinthefer, and C. W. Weekley. 2008. Gap ecology in Florida scrub: Species occurrence, diversity and gap properties. Journal of Vegetation Science 19(4): 503-514.

Reese, W. D. 1984. Mosses of the Gulf South: From the Rio Grande to the Apalachicola. Louisiana State University Press, Baton Rouge, LA, USA.