Celastrus orbiculatus Thunb.

Oriental Bittersweet

Celastrus orbiculatus plant

Family - Celastraceae

Habit - Liana, perennial, sometimes incompletely or completely dioecious.

Stem - Stems to 20 m, twining on other vegetation, circular in cross section. Bark dark brown.

Celastrus_orbiculatus_stemStem.

Celastrus_orbiculatus_twigStem cross section.

Leaves - Alternate, simple, petiolate. Blades variable, even on the same plant, but those on flowering branches usually broadly elliptic to nearly orbicular. Margins toothed, leaf surfaces glabrous or nearly so.

Celastrus_orbiculatus_leavesLeaves.

Celastrus_orbiculatus_leafLeaf abaxial.

Inflorescence - Axillary clusters. Staminate flowers can also be terminal.

Celastrus_orbiculatus_inflorescenceInflorescences.

Flowers - Flowers usually imperfect. Sepals 5, 1.0-1.5 mm long. Petals 5, 3-5 mm long, narrowly oblong, rounded at the tip, greenish. Staminate flowers with 5 stamens, the filaments 1.5-2.0 mm long. Pistillate flowers with minute staminodes, the ovary usually with 3 locules and 2 ovules per locule. Style short, stout, the stigma deeply 3-lobed.

Celastrus_orbiculatus_staminateStaminate flowers.

Celastrus_orbiculatus_staminate2

Fruits - Fruits roughly globose, 8-9 mm in diameter, 3-lobed, dehiscent by 3 valves, these with the outer surface yellow at maturity, the inner surface orangish yellow. Seeds 4-5 mm long, ovoid to ellipsoid, 3-6, each enclosed in a fleshy red aril.

Celastrus_orbiculatus_fruitsFruits in axillary clusters.

Celastrus_orbiculatus_fruits2Fruits.

Flowering - May - June.

Habitat - Bottomland or mesic forest and margins.

Origin - Native to eastern Asia.

Lookalikes - Celastrus scandens.

Other info. - This species of Celastrus is an invader in our state. In many habitats it is more aggressive than the native bittersweet, C. scandens, and has become far more common than the native in some areas. It proliferates by root suckers and can blanket and smother other vegetation. This species is distinguished from the native by its broad, often nearly circular leaves, and also by having most flowers in axillary, rather than terminal, clusters. The fruit valves are also yellow, rather than the orange color of the native's fruit valves. Yatskievych's Flora of Missouri describes the inflorescence clusters as having 2-5 flowers. Although it is easy to find super clusters which greatly exceed that number, this is generally due to multiple clusters being present at a node (each cluster being joined to the main stem by a single peduncle).

As of 2019, collection data do not support the perception that the plant is presently a widespread problem in the state. Vouchered specimens exist from only 14 of Missouri's 114 counties. It is certainly possible that the species is greatly undercollected, but lack of sufficient field work is an impediment to rigorous assessment of the problem. The plant's distribution within the continental U.S. is similarly sporadic. On the other hand, since the plant has spread to at least 14 counties since its first discovery in the state in 1983, there is every reason for concern that it may become a serious problem in the future.

Photographs taken at Babler State Park, St. Louis County, MO, 5-2-2017 and 11-4-2011 (SRTurner).



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