<p>In vegetated landscapes, rain must pass through plant canopies and litter to enter soils. As a result, some rainwater is returned to the atmosphere (i.e., interception, <i>I</i>) and the remainder is partitioned into a canopy (and gap) drip flux (i.e., throughfall) or drained down the stem (i.e., stemflow). Current theoretical and numerical modelling frameworks for this process are near-exclusively based on data from woody overstory plants. However, herbaceous plants often populate the understory and are the primary cover for important ecosystems (e.g., grasslands and croplands). This study investigates how overstory throughfall (<i>P<sub>T,o</sub></i>) is partitioned into understory <i>I</i>, throughfall (<i>P<sub>T</sub></i>) and stemflow (<i>P<sub>S</sub></i>) by a dominant forb in disturbed urban forests (as well as grass- and pasturelands), <i>Eupatorium capillifolium</i> (Lam., dogfennel). Dogfennel density at the site was 56,770 stems ha<sup>−1</sup>, enabling water storage capacities for leaves and stems of 0.90 ± 0.04 mm and 0.43 ± 0.02 mm, respectively. Median <i>P<sub>T</sub>:P<sub>T,o</sub></i> was 72 % (59–91 % interquartile range). <i>P<sub>S</sub></i> data were highly skewed, where mean <i>P<sub>S</sub>:P<sub>T,o</sub></i> was 36.8 %, but the median was 7.6 % (2.8 %–27.2 % interquartile range). <i>P<sub>S</sub></i> variability (<i>n</i> = 30 plants) was high (<i>CV</i> > 200 %) and may be explained by spatiotemporal patterns in <i>P<sub>T,o</sub></i> (since no plant structural factors explained the variability). Mixed dew/light rain events occurred during the study period, revealing that dogfennel can capture and drain dew to their stem base as <i>P<sub>S</sub></i>. Dew-induced <i>P<sub>S</sub></i> may help explain dogfennel's improved invasion efficacy during droughts (as it tends to be one of the most problematic weeds in the southeastern US's improved grazing systems). Overall, dogfennel's rainfall partitioning differed markedly from the site's overstory trees (<i>Pinus palustris</i>), and a synthesis of current literature suggests that these differences may exist across vegetated ecosystems. Thus, more research on herbaceous plant canopy interactions with precipitation is merited.</p>