Here's the description of Alternanthera flavescens (Chaff Flower) from Encyclopedia of Life:
"Herbs, perennial, 6-15 dm. Stems ascending to spreading, often clambering, pubescent, glabrate. Leaves sessile; blade ovate to lanceolate or elliptic, 1.8-8 × 0.5-3 cm, herbaceous, apex long-acuminate or acute, sparsely strigose or glabrous. Inflorescences terminal and axillary, pedunculate; heads yellowish white, subglobose to cylindric, 0.9-2.5(-4) × 0.9-1 cm; bracts keeled, less than 1/2 as long as tepals. Flowers: tepals monomorphic, green, lanceolate, 3.4-4.7 mm, apex acute, villous, hairs not barbed; stamens 5; pseudostaminodes ligulate, margins laciniate. Utricles included within tepals, greenish yellow, ellipsoid, 2.5 mm, apex acute. Seeds ovoid, 1.2-1.3 mm."
Here's another link for that:
http://www.regionalconservatio...
BTW, it says,
"Nectar plant for cassius blue (Leptotes cassius), great southern white (Ascia monuste), long-tailed skipper (Urbanus proteus), Schaus' swallowtail (Heraclides aristodemus) and other butterflies."
Here's yet more info. on it with photos:
http://www.backyardnature.net/...
It also says:
"If you're familiar with waterweeds of the US Southeast you may see a strong resemblance between Yellow Joyweed's flower head and those of Alligatorweed, Alternanthera philoxeroides, which back in 2003, writing from near Natchez, I described as #1 on Mississippi's list of the Ten Worst Invasive Weeds. Alligatorweed, however, forms dense floating mats on lakes and slow-moving streams. That's a long way from growing from a chink in a church's limestone walls."
Another link:
https://books.google.com/books...
These 2 links are for Alternanthera maritima:
https://edis.ifas.ufl.edu/fp03...
http://eol.org/pages/585584/de...
