Lazy Jack Hanging in the Bush

24 Oct

Jack in the Bush, Siam Weed

Chromolaena odorata


John is away for a couple weeks so I must represent alone, although that’s easy after a week of class field trips.   A curious species often encountered in class is Jack in the Bush, a native with a big personality in disturbed places, usually sunny. It is a native in Florida but a mixed minor blessing and major horror escaped invasively around the tropical world.

Jack with violet flower heads (by John Bradford)

Jack with violet flower heads (by John Bradford)

A problem with deliberately introducing plants and beasts—and in some marriages—surfaces when minor blessings later turn into major horrors.   Jack in the Bush has spread far and for different reasons, including during WWII on equipment and personnel, as a living mulch, as a cover crop, and in coffee plantations.   Why is it deliberately spread?   The robust growth crowds out other weeds, is reportedly allelopathic (naturally herbicidal), insect and nematode repellant, and easily generated green manure. It is beneficial to some fallow fields. And being so utterly willing to grow anywhere, our species has attracted attention as a potential cover for mine tailings. Hooray. Bring it!

Jack with white heads (JB)

Jack with white heads (JB)

Too bad it grows too well, and in Africa, India, Asia, and beyond Jack has gone crazy, dominating farm fields, disrupting cropping cycles, invading tree crop plantations, and becoming a general smother as well as hosting pest insects and probably pest fungi. The leaves are petri dishes hosting powdery mildews and many other fungi. Researchers have found the soil near Chromolaena to be oddly high in the spores of certain molds, as if somehow promoting them.

Derisive common names are revealing, such as “King Kong,” “Cholera,” and Rey de Todo (King of Everything) reflecting an imperialistic tendency to form vast single-species stands.

Rey de Todo (See how it looks wilty?)

Rey de Todo

This plant knows how to grow. Is it an annual or perennial? Both. Whatever top growth survives drought, fires, grazers, and mowers from year to year resprouts from buds.   It can regrow directly from the roots, which can enlarge into immortal storage organs, and from tiny seeds (achenes) blowing forth on parachutes to new colonization opportunities as crowded as 2000 seedlings per square meter. Once the growth starts, stand back, as observers have noted, “it grows like a crop.” If the main stem finds a support it can shoot up to 30 feet. If no support is encountered, side branches take over, often growing out at right angles. Growth rates can exceed an inch a day.

The flower heads have an odd trait: variable coloration, whiteish, bluish, violetish, and pinkish. That might tie in with the dozens of butterfly and moth species recorded to visit and pollinate. With so much help the plant can establish anywhere. And who needs butterflies anyhow? It reportedly can set seeds clonally without benefit of bugs.

The plant is wilted when nobody else is.

The plant is wilted when nobody else is.

Reluctant to stand on its own two feet, Jack is sort of a shrub, sort of an herb, and prone to sprawl across and climb more substantial shrubs.   Why form wood when others do it for you? Cut open the stem, even a big one, and you find it to be made disproportionately of pith, soft, cheap, air-filled “styrofoam,” easy, lightweight, and fast to make, and of no substance.

The stem has more soft but useless pith (white) than supportive water-conducting wood (light green).

The stem has more soft but useless pith (white) than supportive water-conducting wood (light green). “Quick & Dirty” No wonder it flops.

That probably explains why Jack in the Bush so often looks wilted.   Water travels in wood (xylem), not in pith (parenchyma). So if your stem is super pithy and deficiently woody, you probably can’t move much water. If you can’t move much water you could spend a lot of time wilted. Ecologist K. Naidoo discussed “severe wilting” of Jack in the Bush as a probable adaptation to help with water use efficiency and avoid leaf damage at times of water stress.

There’s an apparent trade-off in play, just speculating.   Lightning fast growth at the cost of building a soft flimsy stem with minimal water-conducting wood. Let the host plant supply the support, grow like mad when there’s plenty of water, and take it easy wilted in the meantime.


Posted by on October 24, 2015 in Jack in the Bush


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9 responses to “Lazy Jack Hanging in the Bush

  1. Suellen Granberry-Hager

    October 24, 2015 at 11:44 pm

    I didn’t know that Jack in the Bush could have different flower colors. I think we saw only white flowers during class trips last year. The violet ones look like Mistflower or Seashore Ageratum, much prettier than I remember Jack being.

    • George Rogers

      October 25, 2015 at 9:16 am

      I wonder if the different colors represent different genotypes (unlikely, although the species does have recognized “strains”), different conditions, or passing time. Gotta watch more closely, an will

  2. theshrubqueen

    October 25, 2015 at 8:20 am

    We always called it Wild Ageratum and pulled it out quickly. (in North Georgia) I have some here growing in a horrendous environment. Very pithy post!

    • George Rogers

      October 25, 2015 at 9:25 am

      The more horrible-er the better…that’s its job. I’m not quibbling with “wild ageratum,” because in different places in different contexts English names get mixed and matched differently. A lot! If I called a plant wild ageratum here locally, I might be referring to Ageratum houstonianum or Conoclinium coelestinum, but I don’t even know if those grow way up north in arctic GA, so I’m pointing that out merely for local clarity, not to disagree! They all look similar and that can be a basis for slippery-stretchy common names.

      • theshrubqueen

        October 25, 2015 at 6:13 pm

        I prefer Lazy Jack – though I think that is probably the tropic version.

  3. Felicity Rask

    October 25, 2015 at 8:24 am

    You identified this plant for me from a photo. I never saw it in bloom because it got removed by a clean up crew. But I will need to very familiar with both its classy and wited looks in order to keep it in order in an adjoining wildflower patch. Any chance it might be good sauted with garlic and olive oil – butter if one indulges?

    I had to look up ‘mine tailings’ for reassurance! I believe you mentioned growing up in WVA which would explain your use of the term. Felicity Rask


  4. George Rogers

    October 25, 2015 at 9:12 am

    Hi Felicity, Chromolaena comes back happily after removal, so I’ll bet he reappears. If you smoosh the leaves they have a strong chemical odor so ixnay on ibblenay. I’m afraid I know more about mine tailings than many. As kids we used to go to old defunct mine slag heaps to see the smoke coming forth from below looking like and smelling like infernal leakage. Probably still smokin’ after all these years.

  5. Chris Lockhart

    November 2, 2015 at 9:13 am

    Hi George. While working at a little urban scrub preserve in Broward County yesterday, one of my colleagues reminded me of your article. Yikes, that Jack can certainly take over quickly! Where a tree was removed about 18 months ago, it’s now an 7+ ft high dense patch of Chromalaena! Even 6 months ago, it was barely noticeable. Of course, they had an extreme drought there this summer, but it very opportunistically has filled in many nooks and crannies in the preserve since then. Or it began to jump leaps and bounds with a little rain. Not good gopher tortoise salad either. Thanks for your write-up!

    • George Rogers

      November 2, 2015 at 12:36 pm

      Hi Chris, Sometimes the more mundane the plant, the more interesting it is. Sometimes true of people too.


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