05 Jan

Bur Marigold
Bidens mitis (and B. laevis)

Yesterday John and George checked out the plant life along the Halpatioke Trail in a Port. St. Lucie outparcel from Savannas Preserve State Park. The trail touches several habitats from scrub to brook, to brackish shore, and is home to such pleasing species as Partridgeberry (Mitchella repens), Innocence (Houstonia procumbens), and Florida Butterfly Orchid (Encyclia tampensis). John has launched a e-journal of the flora and fauna along that trail. CLICK

Bidens mitis by JB

Bidens mitis by JB

What’s particularly pretty there in early January? A lot, and we had déjà vu all over again with, “what’s that sunny clump of yellow flowers over there by the stream?” Oh yea, of course, Bidens mitis. These are some showy wetland wildflowers.

Up close by JB

Up close by JB

Bidens mitis is similar to another species found locally, Bidens laevis (see below for distinctions) as well as to a species probably in all 48 contiguous states and every Canadian province, but not Florida: Bidens cernua. Yellow-flowered Asteraceae have a way of confounding identification, and all belong to the technical category known in the field as DYCs (danged yellow composites).

Bidens is a large genus, with over 200 species, about nine in Florida. One of the most common weeds is Beggarticks, Bidens alba, identified by its ability to spear its two-pronged seedlike fruits into your pants cuffs. In additional to weediness, Bidens species are known for diverse roles in traditional medicine, and potential involvement in modern pharmacology. Too boring to list here all the ailments countered with Bidens; however, a particularly prominent use is against urinary tract infections. So if you get lost in the woods and suffer a UTI…

These wetland annuals beg a question: In an environment of rising and falling water levels, how do the “seeds” (achenes) know when to sprout and when to sit tight? Mary Leck and colleagues have investigated this in the similar B. laevis. After basic chilling requirements are met (farther north), germination follows light and oxygen levels. Germination is deferred in the dark, in extreme dryness, and under anoxic conditions. Achenes buried and then unearthed enjoy a 19-month window of germination capability. That the window exceeds a year allows for repopulation from the seed bank even after a “bad” year.
Key to similar Bidens species

1. Native to Scranton PA area, invasive intermittently in Florida…Bidens washingtoniensis
1. Native to Florida or adjacent states…2
2. Leaves usually pinnately lobed or compound; teeth on achenes absent or under 1 mm long…Bidens mitis
2. Leaves usually not pinnate, sessile; achene teeth 2-5 mm long…3
3. Ray flower petals > 15 mm long; chaff with orange tips…B. laevis
3. Ray flower petals < 15 mm long; chaff scales with pale yellowish tips…B. cernua (not in FL)

Bidens washingtoniensis

Bidens washingtoniensis

Data source for B. laevis germination: Leck et al., Bull. Torrey Bot. Club 121: 230-239. 1994.


Posted by on January 5, 2013 in Bur Marigold


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7 responses to “Bur-Marigold

  1. SmallHouseBigGarden

    January 5, 2013 at 10:40 pm

    I must say that B.washingtoniensis is probably my least favorite variety!
    Great post! I love learning about the local flora; I’ve got tons of info gaps being a newish Vero Beach resident and you sre def helping me fill things in!

    • George Rogers

      January 6, 2013 at 9:05 am

      Vero is a great place to enjoy the local flora. My parents used to be Vero snowbirds, and the natural areas around there are lovely. And then of course McKee Gardens is a joy to explore, even if not native-o-centric.

  2. Martin

    January 6, 2013 at 8:18 am

    Aw… poor ol’ Joe! Why Joe don’t git no love?

  3. George Rogers

    January 6, 2013 at 9:05 am

    Because he’s not in tune with the native flora.

  4. Mary Hart

    January 7, 2013 at 3:40 am

    My favourite UK marsh flower is Marsh marigold or Kingcup Calutha palustris, with its big, bold flowers. After the weather we’ve had this winter I reckon the whole country could become covered with them!!

  5. George Rogers

    January 7, 2013 at 10:11 am

    Mary, Me too! It’s not in S. Florida, but is an old friend from Michigan. Remarkably similar in appearance. I hope they brighten your world this spring. Actually hot here today—people are complaining about the heat if you can believe it.

  6. My An Le

    November 20, 2015 at 10:21 am

    My dad grew some Bur-Marigold in the backyard. These attract bees like crazy, but they are so cool to look at and photograph.


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