Vascular Plants of Williamson County

Hydrocotyle umbellata [Araliaceae/Apiaceae]
umbrella water pennywort

Hydrocotyle umbellata L., umbrella water pennywort. Hydrocotyle umbellata — UMBRELLA WATER PENNYWORT [Araliaceae/Apiaceae] Perennial herb, rhizomatous, fibrous–rooted at nodes, lacking aboveground stems, with erect to ascending leaves and flowering shoots, in range to 25 cm tall; shoots with only cauline leaves, glabrous, lacking any distinctive odor; rhizomes cylindric, 1.2—1.5 mm diameter, white, internodes often 20—60 mm long, with tuberlike swelling at node; adventitious roots many at nodes.


Leaves alternate, simple and umbrellalike (peltate), long–petiolate, with stipules; stipules 2, attached to stem, broadly triangular, 2—3 mm long, scarious and brownish; petiole cylindric, 130—260 × 1—3 mm, white belowground and green aboveground; blade round, 13—63 mm, shallow and broad, subequal lobes, lobes closely spaced, sometimes with a pair of lobes overlapped at base, crenate on lobe margins, palmately veined to each lobe, with 12—16 principal veins from center, upper surface glossy.


Inflorescence condensed raceme, axillary, of 30+ helically alternate flowers at tip of long, unbranched axis, at anthesis 10—15 mm across, bracteate, glabrous; peduncle same length as petiole of associated leaf; rachis internodes short; bractlet subtending pedicel cupped boat–shaped, 0.7—1.2 mm long, colorless with green vein, persistent; pedicel spreading to ascending, at anthesis 4—5.5 × 0.25 mm increasing 2× in fruit.


Flower bisexual, radial, 3 mm across; sepals absent; petals 5, spreading at anthesis later deflexed, triangular–ovate, 1 × 0.7—0.8 mm, white to greenish white, 1–veined, without midridge, abscised in developing fruit; Stamens 5, free, alternate with petals; filaments spreading, ± 0.5 mm long, white; anthers dorsifixed, dithecal, ca. 0.45—0.5 mm long, yellowish green aging yellow, longitudinally dehiscent; pollen yellow; pistil 1; ovary inferior with ± fleshy, cushionlike platform (stylopodium, stylar tissue) on top having 2 semicircular halves 0.5—0.7 mm, pale green with minute purplish speckles, ovary semicircular in outline and compressed ⊥ septum, 1.2—1.3 × 1.2—1.3 mm, green, with 3 ribs on each side and 1 on each edge, 2–chambered, each chamber with 1 ovule; styles 2, arched inward, ± 0.4 mm long, white or pale green; stigmas terminal, minute.


Fruit schizocarp, of 2 dry 1–seeded halves (mericarps), mericarps D–shaped in outline strongly compressed, ± 2 × 1.4—1.6 mm, ca. 0.7 mm thick on margin with fruit wall unevenly thickened around seed, weakly ribbed, glabrous; carpophore absent.


Seed D–shaped and compressed side–to–side, ca. 1.2 mm long, firmly attached to fruit wall.

A. C. Gibson