Sium suave Walt.

Sium suave plant

Sium suave plant

Family - Apiaceae

Stems - Stout, glabrous (entire plant), herbaceous, hollow, ribbed and angled, to 2m tall, slightly zig-zag in form, erect but reclining with age, branching, from thickened roots, rooting at lower nodes, with a sweet fennel fragrance.

Sium suave stemStem.

Leaves - Alternate, odd-pinnate, petiolate to sessile. Lowest leaves to +50cm long, reduced above. Petiole to +7cm long, sheathing, ribbed or angled, with an adaxial groove. Lateral leaflets sessile, opposite, linear to lanceolate or lance-ovate, to +/-15cm long, 6cm broad, serrulate to serrate, deep green adaxially, lighter shiny-green abaxially, glabrous, acute to acuminate at apex, larger leaflets typically rounded and oblique at the base. Terminal leaflet with a petiolule to +3cm long.

Sium suave leaf"Typical" basal leaf.

Sium suave leafCauline leaf with thin leaflets.

Inflorescence - Terminal and axillary compound umbels. Peduncles to +6cm long, ribbed and angled. Primary rays to 3.5 cm long, subtended by recurved bracts, glabrous. Bracts to -2cm long, 2-3mm broad, linear-lanceolate to lance-attenuate, with scarious margins, +/-12. Umbellets with raylets to 8mm long, subtended by similar but smaller bracts than main rays. Raylets to 8mm long, glabrous. Umbellets with 25-35 flowers.

Sium suave inflorescenceInflorescence.

Sium suave inflorescenceBracts at base of rays.

Flowers - Petals 5, white, spreading, glabrous, obovate, with an inflexed apiculate apex, to 1.5mm long, 1.3mm broad. Stamens 5, alternating with petals, spreading. Filaments white, to 2mm long. Anthers whitish-pink to pink or yellow, .2mm broad. Styles 2, distinct, very short, -.2mm long, with greenish-white stylopodium. Stylopodium to 1.1mm broad. Ovary inferior, ribbed, -1mm long in flower, 1.1mm broad, compressed slightly. Fruit oval to orbicular, to 3mm long.

Sium suave flowers

Flowering - July - September.

Habitat - Wet areas.

Origin - Native to U.S.

Other info. - This highly variable species can be found throughout Missouri in wet habitats. As seen in the pictures above, the plant is very variable and can be hard to ID in the field. The characteristics to look for are the bracts and bracteoles subtending the rays and raylets of the inflorescence and the serrulate to serrate margins of the leaflets.

Photographs taken at Buffalo Creek, Mark Twain National Forest, Ripley County, MO., 6-30-00, and in Brown Summit, NC., 7-29-02.


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