Photo by Bruce Kirchoff licensed under CC BY 2.0

I sure do love me a good oak. Moving to the Midwest of North America has given me the opportunity to meet many new oak species. One oak that has captured my attention in recent years is the overcup oak (Quercus lyrata) whose both common and scientific names first attracted me to this wonderful tree.

Let’s start by looking at the scientific name of this species. The specific epithet “lyrata” was given to this tree because its leaves are said to resemble a lyre. Having no familiarity with popular instruments of Ancient Greece, I had to look this one up. Personally, I have a hard time seeing the resemblance in most leaves. Perhaps this is because the leaves on any given tree can be highly variable in both shape and size depending on both where they are positioned in the canopy and where the tree itself is rooted.

The name “overcup” comes from the fact that the caps of each acorn nearly encompass the entire seed. It is neat to see a mature acorn of this species as they appear to be immature at all stages of development. The odd morphology of these acorns has everything to do with where these trees grow in nature and the way in which they manage seed dispersal.

Overcup oak is one of the most flood tolerant oaks in all of North America. In fact, it most often grows in around wetlands and in floodplains throughout south-central portions of the continent. As such, this species has evolved to tolerate and take advantage of periodic flooding from one year to the next. Not only can mature trees handle weeks of having their roots and trunks completely submerged, the overcup oak also utilizes flooding as a means of seed dispersal.

The cap that covers each seed is very corky, which causes the acorns to float. This is good news for the seeds as young trees have a hard time making a living in the shade of their parents. Historically, floods would pick up and move overcup acorn crops and, with any luck, deposit the acorns in a new floodplain where disturbance has cleared enough spots in the canopy for the acorns to germinate and grow into vigorous young saplings.

Speaking of germination, overcup oaks are unique among the white oak tribe in that their seeds exhibit a prolonged dormancy. Normally, acorns of the various white oaks germinate in the fall, not long after they were shed from the trees above. However, living in areas prone to flooding would make germinating at that time of year a risky endeavor. As such, overcup oak acorns lay dormant for months until some environmental cue(s) signals enough time has passed.

Overcup oak is also extremely intolerant of fires. Even modest sized burns can severely damage or kill all but the largest individuals. Normally, the forests in which these trees grow are too wet to produce large fires but prolonged droughts and altered flood regimes can change those dynamics to such a degree that large swaths of overcup oak can be killed.

In fact, altered flooding regimes are one of the biggest threats facing overcup oaks in their native range. Because we have dammed, diverted, and channeled so many waterways in North America, the floods that once maintained overcup oak habitats have changed in a big way. Without regular flooding to disperse their seeds and reduce competition from the canopy above, overcup oaks are having a much harder time regenerating. Saplings gradually dwindle in the shade of their parents and, where rivers do continue to flood, these events are often much more severe than they were in the past. Saplings that aren’t tall enough to rise above the floodwaters eventually drown. Overcup oak may be tolerant of flooding but it is by no means its preferred way to live.

Despite these challenges, overcup oak is still a prominent member of seasonally flooded forests throughout its range. It is a magnificent species well worth spending the time to become familiar. It can also make an excellent specimen tree in all but the driest of south-central North American soils. Also, because it is an oak, this incredible species is also chock full of wildlife value, making it an important component of the ecology wherever it is native.

Photo Credits: Bruce Kirchoff [1] [2] (Licensed under CC-BY), U.S. Geological Survey, Chhe, USDA

Further Reading: [1] [2] [3]

The pine lily (Lilium catesbaei) is one of North America’s finest species of lily. It produces the largest flowers of the genus on this continent and to see one in person is a breathtaking experience. The pine lily is endemic to the Southeastern Coastal Plain where it prefers to grow in mesic to wet flatwoods, wet prairies, and savannas. Though it enjoys a relatively wide distribution, today it rarely occurs in any abundance.

The pine lily’s rarity may be a relatively recent status change for this wonderful plant. Historical records indicate that it was once quite abundant in states like Florida. Today it occurs in scattered localities and predicting its presence from year to year has been a bit tricky. Indeed, the pine lily appears to be very picky when it comes to growing and flowering.

One aspect of its biology that might lend to its limited appearance is the fact that it can remain underground in a dormant state for years. Like other members of this genus, the pine lily emerges from a bulb. This underground storage structure is small by lily standards, which means that most pine lilies are operating on marginal stores of energy in any given year.

Some have estimated that individual bulbs can remain dormant for upwards of 5 years before the right conditions for growth flowering present themselves. Of course, such dormancy can be a nightmare for proper conservation of such a unique plant. Aside from the individual flower borne at the tip of a long, slender stem, the rest of the plant is very dainty. In fact, its flowers can be so heavy compared to the rest of the plant that some stems simply topple to the ground before they can set seed. The slender stem, small leaves, and tiny bulb equate to a small operating budget in terms of energy stores. That being said, we are starting to get a clearer picture of what pine lilies need to thrive and it all comes down to fire.

Photo by Eleanor licensed by CC BY-NC 2.0

The key to acquiring enough energy for growth and reproduction appears to be a proper amount of sunlight. Without it, plants languish. This is where fire comes in. The pine lily lives in a region of North America that historically would have burned with some frequency. Wildfires sweep through an area, burning away competing vegetation like saw palmetto (Serenoa repens) and clearing the ground of accumulated debris like sticks and leaves. By burning away the competition, fire creates open areas where delicate plants like the pine lily can eke out an existence. Indeed, research has shown that pine lilies produce more flowers and seed immediately following ground-clearing burn followed by a subsequent decline in flowering and seed set as the surrounding vegetation begins to grow back.

If a pine lily does have enough energy to flower, then one of the most stunning flowers in all of North America is presented with its face towards the sky. Its 6 large petals are brightly colored and taper down into what looks like tiny tubes. Nectar is produced within these tubes and, coupled with the bright coloration, attract numerous insect visitors.

Not all insects are capable of successfully pollinating such a large flower. In fact, it would appear that only a couple of species take up the bulk of the pollination of this incredible plant. As far as we know, the Palamede swallowtail butterfly (Papilio palamedes) and perhaps the spicebush swallowtail (P. troilus) are the only species large enough to properly contact both anthers and stigma while feeding at the flowers. The large wingspan of these butterflies do all of the work in picking up and depositing pollen. All other insects are simply too small to adequately achieve such feats.

Though we still have a lot more to learn about the pine lily, what we do know tells us a story that is repeated for fire-dependent ecosystems throughout the world. Without regular disturbance from fire, biodiversity drops. The pine lily is not alone in this either. Its fate is intertwined with countless other unique plant species that call the coastal plains their home.

Photo Credits: [2]

Further Reading: [1] [2] [3]