Common Buckthorn - Rhamnus cathartica

Here is a month-by-month outline of the life cycle stages of woody invasives in Southeast Michigan, framed entirely in ecological/phenological terms. focusing only on growth, reproduction, and dormancy patterns that matter for understanding how this species behaves through the year.

January – February

• Plants remain fully dormant.

• Leaves are absent; branches retain their twigs

• Mature shrubs often hold onto persistent berries from the previous fall.

• Roots remain alive and ready to resume growth when soil temperatures rise.

March

• One of the earliest woody species to break dormancy.

• Sap begins to flow before many natives.

• Swelling of buds occurs as day length and temperatures increase.

April

• Leaf-out begins, typically earlier than most native shrubs and trees.

• The plant gains a head start on photosynthesis while native species are still bare.

• Root growth also resumes actively in warming soils.

May

• Vigorous shoot elongation continues.

• Often flowers before many native shrubs flower.

• Flowering occurs while leaves are fully expanded, taking advantage of high light conditions before canopy closure.

June

• Fertilized flowers develop into small green berries.

• Leaf canopy is fully developed, dense, and shade-producing.

July – August

• Berries enlarge and turn green to appropriate color

• Shrubs maintain dense foliage, often shading out herbaceous understory growth.

• Stems continue secondary thickening; root reserves build steadily.

September

• Fruits ripen and persist into fall.

• Leaf canopy remains dense while many natives begin senescing.

• Seeds are viable and ready for dispersal. Birds and mammals begin consuming fruits, dispersing seeds across the landscape.

October

• Leaves remain green much later than most native trees and shrubs.

• Fruits continue to be available and dispersed.

• Delayed senescence provides continued photosynthetic advantage compared to natives.

November

• Leaves may still be present after most native species have dropped theirs.

• Eventually, hard frosts trigger leaf drop, though often weeks later than native woody plants.

• Roots store carbohydrates over winter, supporting next year’s early growth.

December

• Plants are bare of leaves.

• Berries may persist into early winter, continuing to be dispersed by birds.

• Stems and roots remain dormant, maintaining stored reserves.

Key Ecological Notes

• Extended growing season: Leaf-out occurs early (March/April) and senescence occurs late (October/November), giving the plant several extra weeks of photosynthesis compared to native shrubs.

• Seed dispersal: Fruits ripen in fall (September onward) and remain available through winter, ensuring continuous dispersal.

• Growth strategy: Dense foliage, rapid spring development, and late persistence create strong competitive suppression of native species.

When you scrape the bark, it is orange underneath - larger diameter only

Round black berries in the fall (male plants only)

Small thorns near the tip of the branch. The tip of the branch looks like a deer hoof

Lenticels in the bark (more noticable in smaller common buckthorn plants

HABITAT—C. Buckthorn prefers part-sun and neutral to alkaline soilsbut can grow in a wide range of conditions. It tolerates well-drained sand to poorly-drained clay soils, and full sun to full shade. C.  Buckthorn invades upland habitats including open woods, woodland edges, old fields, and roadsides. It can survive in flatwoods, fens and other wet habitats, but is less frequent (see Glossy Buckthorn).

In the OOR, C. Buckthorn has been found on sand dunes, upland and swamp forests, within and at the edges of floodplains and streams, near vernal pools and ponds, and along roads and ditches.

IDENTIFICATION—Habit: Deciduous multi-stemmed shrub, becoming a single-trunked tree with age. Typically reaches heights of 10-25’, and DBH ~4”, but has been recorded in MI at a height of 61’! DBH has also been recorded as high as ~10”!

Leaves: Simple, with toothed margins. Oval and 1-2.5” long with pointed tips. Leaf veins are prominent, paired (3-5 pairs), and curve close to the leaf tip. Sub-opposite arrangement. Hairless. Dark green on top, lighter green below. Pale yellow in the fall. 

Stems: Young bark is brown and shiny with prominent lenticels. Becomes gray and scaly, to peeling with age. Branches have light, vertical, raised marks. Slender, smooth twigs, often with a 0.2-0.9” thorn at the tip. Yellow sapwood and pink-orange heartwood.

Flowers: Small (1/4”), with four petals. Greenish yellow and clustered in the leaf axils. Fragrant. Dioecious.

Fruits: Small and round, 1/4” in diameter. Ripen from green to purplish-black. Unripe fruits contain a laxative called emodin. Each contains 1-5 seeds which have a deep, narrow groove on back.

Seeds: 4-5 mm long and narrowly grooved. High germination rates. 15,000-54,000 seeds produced per plant per year.

Roots: Shallow and fibrous. Extent can vary. A mature C. Buckthorn in North Dakota had roots 18.5’ long, but 99% were in the top 3’.

Black Cherry - similar to larger Common Buckthorns

Choke Cherry - similar to smaller Common Buckthorns