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Coastalplain Golden Aster and the Florida Marcescent Lifestyle

09 Oct

Chrysopsis scabrella

Asteraceae

Golden Asters in the sun (John Bradford)

Golden Asters in the sun (John Bradford)

Every time John and I botanize through an open scrubby area, such as today, we enjoy an odd-looking species, Coastalplain Golden Asters rising awkwardly from the white sand at varied angles to attain irregular heights. Very martian! To add drama, the funny stems retain a covering of dead withered foliage, more properly called “marcescent” leaves.

The dead leaves stay put.

The dead leaves stay put.

Dead leaves usually fall away and decay in most plants, but not always. The Golden Aster appearance always evokes the same old memory for me. Back in the Reagan Administration I had the good fortune to work at high elevations in South America where several unrelated plants resemble Golden Aster by having marcescent leaves covering an otherwise bare stem.   Around the world, this life form has evolved repeatedly, usually in exposed habitats where a drying risk is coupled with fluctuating temperature extremes, often intermittent frost alternating short-term with warm temperatures. Of a few examples here in South Florida,  Golden Aster is the most striking.   (We’ll look at Rabbit Tobacco another day.)

Coastalplain Golden Aster is generally described as a “biennial,” hunkered down the first year as a rosette on the ground, with the stem then rising the second year to flower and fruit.   New rosettes form at the stem base.   I’m not 100% sure the plant always obeys its biennial characterization.

Here is Espeletia in Ecuador:  CLICK

Here is Golden Aster in Stuart, Espeletia Jr.:

Every stem with a skirt of marcescent leaves.

Every stem with a skirt of marcescent leaves.

We might say blithely, “well, the dead leaves protect the stem.”   OK, but exactly how, from precisely what?   If anyone has looked into it at a physiological level in Chrysopsis, I can’t find it. But botanist Alan Smith back in the 70s took a hard look at Espeletia in Venezuela, and provides inspiration for a better look at our similar local case. Dr. Smith found the Espeletia habitat to feature strong seasonal differences in rainfall, like us. And there were wide strong short-term temperature fluctuations, like us. The greatest temperature stress and moisture stress occurred during the dry season, likewise the case in Florida if the main temperature stress is frost. (We live near the southern limit of the all-Florida geographic range for Chrysopsis scabrella.)

Smith and other botanists have interpreted marcescent leaf blankets as a buffer against fluctuating temperature extremes. Removal of the dead leaves cost a lot of Espeletias their lives.   The main apparent reason was that during times of frosty nights alternating with warm days stems with their dead leaves intact never dipped below freezing, whereas the ones with marcescent leaves removed dipped and died. Those dead old leaves don’t radiate heat at night.

It may seem odd to speculate that frost protection might be the “main” benefit of marcescent leaves, especially in a plant like Golden Aster so obviously exposed to extreme drying.   Don’t those dead leaves merely protect the stem from hot dry winds? Maybe, but two reasons suggest otherwise:

A.  In general, water loss from stems is not severe.   The stem probably does not need much protection from direct drying.  (Cacti are all-stem.)

B. Frost stress is drying stress. One of the worst aspects of frost for a plant (in a not-very-frosty borderline setting) is that freezing in the stem diminishes water passage from the roots to the leaves. An plant in a super-dry setting with temperatures hitting 80 degrees by day and dipping below freezing by night has much to fear from Jack Frost.   The warm day, especially at dawn, creates high demand for water to the living leaves, but if frost-impaired stem tissue can’t deliver, well that’s tragic.  Walking through the scrub in 90 degree weather and 90 percent relative humidity, it takes some faith to see those stem-blankets of dead leaves as possible winter coats.

Fruiting heads (John Bradford)

Fruiting heads (John Bradford)

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10 Comments

Posted by on October 9, 2015 in Uncategorized

 

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10 responses to “Coastalplain Golden Aster and the Florida Marcescent Lifestyle

  1. Sally Hart Brodie

    October 10, 2015 at 9:14 am

    All of your topics are fascinating and not covered anywhere else I read. Thank you for this wonderful little treat. I will be looking for it in the scrub.

     
  2. George Rogers

    October 10, 2015 at 9:48 am

    Hi Sally, so nice to hear from you. Right—it’s one of those plants that make it so fun and interesting. I often feel that as a botanist, teacher, and nature-enjoyer we tend collectively to put too much emphasis on the spectacular, or the rare, or the exotic, or whatever’s “cool,” when the authentic experience is what we see easily, every day. Spoken like a full fuddy-duddy.

     
  3. Felicity Rask

    October 10, 2015 at 10:12 am

    Generally, when I read of exotic places, I’m inclined to think about the birds I didn’t know enough to look for. Here it is reversed, when I was high in the Andes (actually during Kennedy’s Administration) I thought only of looking for the Condor. I didn’t miss the exotic plants but didn’t know anything about naming them. I think I have noticed this ‘marcescent’ lifestyle on many plants because, it is on the whole, unsightly. Is it also what one sees on plants such as undisturbed Sabal palmetto? Felicity in rapidly cooling VA. >

     
  4. George Rogers

    October 10, 2015 at 10:48 am

    Hi Felicity, Searching for condors in the Andes would “hit the spot” with me. A week ago today while in a boat I got to see an eagle swoop down and snag a fish—like something from the Discovery Channel. I love it in the Andes, if a passing bus doesn’t knock you off the narrow mountain road into the valley so very far below. Washingtonias might be a more dramatic example of a marcescent palm, although cabbage palms, such as the one in my yard, develop a skirt of dangling dead leaves, usually though at the top of the stem, not covering the entire trunk? Not that we get to see natural cabbage palms in urbia/suburbia often, because somebody out there decided that all cabbage palms should have a haircut, leaving only their topmost leaves, removing all those nice dead leaves, and many of the nice lower living leaves. (However, I am not trying to start a discussion of palm pruning…today I’m focused on scrub plants.)

     
  5. Steve

    October 19, 2015 at 10:15 am

    Great article, and I learned a new term. Could the marcescent leaves enhance the plant’s fitness by providing extra surface area for dew collection, in these arid places? Another marescent species we have down her along the coast is Sea Lavender (Argusia gnaphalodes).

     
    • George Rogers

      October 19, 2015 at 10:24 am

      Hi Steve, good point about dew, and nice example on the Sea Lavender out there on the sand where protection maters. Although the leaves are dead, they just might be able to take in some water. (Given that xylem is dead tissue some intake is conceivable.) And they sure can collect dew and funnel it to the stem and root crown externally. Even more certain, they protect tender tissues below from drying, a benefit of dew-soaked leaves…which also might help with a little evaporative cooling. Relevant to all this, the Chrysopsis hides its new basal growth among those potentially moist dead leaves. And, although not to my knowledge in FL, at least one marcescent-leaf species is documented as sending little feeder roots out of the stem into the leaf coating.

       
      • Steve

        October 19, 2015 at 10:35 am

        Yeah, it could be a dew or die circumstance.

         
  6. George Rogers

    October 19, 2015 at 10:44 am

    In my classes it is due or die

     
  7. friedova

    March 2, 2016 at 1:12 pm

    That is better than “doh or die”. Entertaining, and educational as always. The mundane and ordinary are neither! Great photos, John. Spring is happening here in Dunnellon. The Jessamine is in full fragrant bloom. Wax Myrtles and various other shrubs/trees showing lots of new life.

     
  8. George Rogers

    March 2, 2016 at 1:24 pm

    Yep, suddenly a “burst of spring” even here in PBC. Thanks and get out the Frisbee!

     

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