Rorippa sessiliflora (Nutt. ex Torr. & A. Gray) Hitchc. - Sessile-flowered Cress

Rorippa sessiliflora plant

Family - Brassicaceae

Stems - From long, thick, white roots, glabrous, to +60cm tall, becoming purplish in strong sun, ridged, branching in the upper half, herbaceous, erect, fistulose.

Rorippa sessiliflora stem

Leaves - Alternate, petiolate, glabrous. Basal leaves pinnatifid, to 10cm long, 2-3cm broad, divided almost all the way to the midrib. Divisions rounded to subacute, with a minute mucro. Leaves becoming less divided towards and smaller towards the apex of the plant. Leaf tissue cuneate all the way to the base of the petiole and forming two small auricles at the base of the petiole.

Rorippa sessilifolia leaves

Inflorescence - Terminal and axillary racemes, compact in flower, quickly elongating in fruit to +/-15cm long. Rachis of the inflorescence glabrous. Pedicels of the flowers 0-1mm long, to 2mm long in fruit, typically spreading perpendicular to the stem in fruit.

Flowers - Sepals 4, pale yellow, erect, 2mm long, .5mm broad, glabrous, rounded at the apex, slightly inflated, fugacious. Petals absent or very minute, when present the petals are spatulate, -2mm long, .5mm broad, glabrous, translucent yellow, fugacious. Stamens 4, erect. Filaments glabrous, 2-2.2mm long, translucent-white. Anthers yellow, .3-.4mm broad. Ovary green, glabrous, 1-2mm long in flower, -1mm in diameter, cylindrical, quickly expanding. Style absent. Stigma capitate, .8mm broad. Siliques cylindrical, glabrous, beaked by the persistent style and stigma, to 1cm long, 2-2.5mm in diameter, 2-valved, many-seeded.

Rorippa sessilifolia flowersFlowers.

Rorippa sessilifolia fruitsFruits.

Flowering - April - October.

Habitat - Bottomland forests, banks of streams and rivers, sloughs, levees, railroads and roadsides.

Origin - Native to U.S.

Other info. - This species can be found scattered throughout Missouri but is absent from much of the central Ozark region. Yatskievych speculates that this absence may be due to the lack of muddy habitats in this region.
R. sessiliflora can be identified by its habitat, divided lower leaves, minute flowers, and many-seeded fruits. The short pedicels of the fruit are the shortest of any Rorippa species in the state.

Photographs taken at Davis Ferry, Monroe County, AL., 3-26-06.


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