8. Gratiola L. (hedge hyssop)

Plants annual or perennial herbs, with fibrous roots, terrestrial or emergent aquatics in shallow water, sometimes with rhizomes. Stems erect or ascending, less commonly spreading with ascending tips, then rooting, at least at the lower nodes, bluntly to sharply 4-angled near the tips, but rounded for most of their lengths, glabrous or glandular-hairy, sometimes only toward the tips, sometimes swollen and spongy toward the bases. Leaves opposite, sessile. Leaf blades not thickened or leathery, variously shaped, those of submerged leaves sometimes much narrower than the others, unlobed, mostly bluntly to sharply pointed at the tip, variously tapered to rounded at the base, sometimes clasping the stem, the margins entire or toothed, mostly above the midpoint, the venation palmate with 3 or 5 main veins, the surfaces glabrous or variously hairy, not shiny, the undersurface usually inconspicuously gland-dotted. Inflorescences axillary, the flowers 1 or 2 per node, the flower stalks short to elongate; bractlets 2, closely subtending the calyx, sepaloid. Flowers perfect. Calyces becoming somewhat enlarged at fruiting, deeply 5-lobed nearly to the base, glabrous or more commonly glandular- or nonglandular-hairy, the lobes subequal, variously shaped. Corollas bilabiate, 5-lobed, but sometimes appearing nearly 4-lobed, more or less tubular to somewhat trumpet-shaped, the tube longer than the lobes, usually slightly arched upward, white or cream-colored to pale yellow externally (occasionally pale lavender-tinged) with dark purple to dark brownish purple venation, white to pale pinkish-tinged or light yellow in the throat, spurless, the throat open, hairy on the inner surface of the upper side, the upper lip nearly straight to somewhat recurved very shallowly notched or 2-lobed, the lower lip straight to somewhat spreading or slightly arched upward, with 3 deeper lobes, these usually shallowly and broadly notched (the lowermost lobe sometimes with a pair of minute notches), the lobes usually white, often becoming purplish-tinged upon drying. Fertile stamens 2, the filaments not exserted, the anthers positioned on the expanded, flattened, membranous filament tip, the anther sacs parallel; staminodes usually present, appearing as a pair of antherless filaments. Style 1, not exserted, forked near the tip, the short branches flattened and broad (appearing similar to a pair of lips). Fruits capsules, ovoid to globose, glabrous, the 2 locules equal in size, dehiscent longitudinally along the 2 sutures and often also between them (then appearing 4-valved). Seeds numerous, 0.5–0.9 mm long, more or less cylindric to somewhat conic, not flattened, but usually appearing several-angled, the surface yellowish brown to brown, with a network of prominent ridges, these arranged into vertical ranks. About 25 species, nearly worldwide.

Rahmanzadeh et al. (2005) suggested that Gratiola, Bacopa, Mecardonia, and thirteen other non-Missouri genera of the Scrophulariaceae tribe Gratioleae should be segregated into a separate family, Gratiolaceae, based on a limited sampling of taxa for molecular analysis. However, they indicated that the group is closely allied to the Plantaginaceae lineage, and most recent authors have continued to interpret it as part of that family (Olmstead et al., 2001; Tank et al., 2006; Judd et al., 2008, Angiosperm Phylogeny Group, 2009). As noted by Tank et al. (2006), the systematics of this group are still not well understood.