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comparison between Xyris iridifolia (left) and Xyris difformis (right).
first photos show the difference between the shape of the spikes, and the broad flattened scape of iridifolia versus the narrowly winged scape of difformis, highlighted by the sunlight in pic 2.
3rd photo compares habit — iridifolia taller, with longer and much broader leaves; difformis shorter, with narrower leaves.
4th pic shows seed difference — elongate and dark grey in iridifolia, rounded and pale yellow in difformis.
both found together in bottomland forest, as typical; creek in background

heads congested at tips of lateral branches, inflorescences not densely leafy; involucres 4-5 mm high; leaves oblanceolate to elliptic, margins entire or inconspicuously toothed; rays white and drying lavender and >20, stems mostly glabrous, rhizomatous perennial, phyllaries not subulate tipped, disc flowers 4-6 mm long

Gravel parking lot at golf course. Culm 15cm. Fibrous roots, annual. All leaves are cauline, 25mm x 2mm. Ligule ciliate. Inflorescnce a panicle 5cm x 3cm. Spikelets 7mm x 1.5mm, 12-15 florets. 1st glume 1mm, keeled. 2nd glume 1.5mm. Lemmas 2.5mm, strong green lateral vein. Pedicels all shorter than spikelet. Caryopsis 0.6mm x 0.3mm, no groove. 2 stamens I think.

Key breaks(Illust. Fl. or E. TX):
Achene trigonous/styles 3-branched
Spikelets in each group arising from the same point
Leaves well developed
Scales of spikelets with tips not reflexed
Scales > 1mm long
Plants large perennials
Scales 2 keeled at base
Leaf blades, bracts, etc not nodulose
Culms smooth to the touch
Inflorescence bracts all horizontal to ascending, none like a continuation of the culm
Spikelets 10mm long, (2mm wide) achenes broadly ellipsoid,(with acuminate beak, narrow stipelike base, honeycomb surface), approx. 1.3mm long.
(lower florets maturing, shedding scales + achenes as upper ones develop)