Common Trees in Pennsylvania: Identification Guide

Eastern Hemlock (Tsuga canadensis)

The eastern hemlock is Pennsylvania's state tree and one of its most ecologically significant, forming dense, cathedral-like stands in the cool, moist gorges and north-facing slopes of the Appalachian ridges — creating unique microclimates that support rare plants, cold-water fish streams, and specialist songbirds like the Blackburnian warbler and Louisiana waterthrush. Cook Forest State Park in Clarion County and Ricketts Glen State Park in Sullivan County protect some of the finest old-growth hemlock stands in the eastern United States, with individual trees exceeding 500 years of age and 150 feet in height. Unfortunately, the hemlock woolly adelgid (Adelges tsugae) — an invasive insect from Asia — has caused catastrophic hemlock mortality across the Ridge and Valley and southern Appalachian regions of Pennsylvania, threatening to eliminate this keystone species from much of its range. Conservation efforts focus on biological control using predatory beetles and targeted insecticide treatment of high-value stands.

Where to find it: Cool, moist north-facing slopes, stream gorges, and ravines throughout the Appalachian Plateau, Ridge and Valley, and northern Piedmont

How to identify it:

• Short, flat needles 0.5–0.75 inch long with two white stripes on the underside, arranged in a flat, two-ranked pattern on branchlets
• Small, delicate, oval cones about 0.75 inch hanging from branch tips
• Drooping, feathery branch tips giving the whole tree a graceful, cascading appearance
• Deeply furrowed, gray-brown bark developing into broad, flat-topped ridges on old trees

Tulip Tree (Liriodendron tulipifera)

The tulip tree is Pennsylvania's tallest native hardwood and one of the most ecologically and economically important trees in the state, growing to magnificent size — often exceeding 150 feet in height and 6 feet in diameter — in the rich, moist coves and slopes of the Ridge and Valley and Piedmont regions. In Pennsylvania's original pre-settlement forests, tulip trees formed the dominant canopy in moist, fertile sites throughout the southern half of the state, and historical accounts describe trees of extraordinary size along the Susquehanna, Delaware, and Lehigh valleys. The state's timber industry valued tulip tree (also called yellow-poplar) highly for its straight, clean grain and workability. The striking tulip-shaped flowers in May and early June are beloved by ruby-throated hummingbirds and are often seen high in the canopy against the sky.

Where to find it: Moist, fertile coves, lower slopes, and floodplain borders throughout the Piedmont, Ridge and Valley, and southern Allegheny Plateau

How to identify it:

• Distinctive 4-lobed leaf with a flat or concave tip — unlike any other Pennsylvania tree
• Large, tulip-shaped flowers with 6 pale green-yellow petals and an orange interior ring, May–June
• Straight, columnar trunk with deeply furrowed, interlacing gray-brown bark
• Upright, cone-like aggregate of winged seeds persisting on bare branches through winter

White Oak (Quercus alba)

White oak is Pennsylvania's single most ecologically important tree species — a keystone of the state's upland oak-hickory and mixed oak forests, producing abundant acorn mast every three to five years that drives wildlife population dynamics across the state for deer, bears, turkeys, and dozens of other species. The trees grow to remarkable size and longevity on Pennsylvania's ridges and slopes, and several champion white oaks in the state have stood for over 400 years. Pennsylvania's Wissahickon Valley, Brandywine Creek corridor, and many state forest tracts harbor fine examples of old white oaks with massive, horizontally spreading crowns. White oak is the premier wood for whiskey and wine barrel production — its relatively tight grain limits alcohol seepage — and Pennsylvania sawmills have historically served this market.

Where to find it: Dry to mesic upland slopes, ridge tops, and well-drained terraces throughout Pennsylvania's Ridge and Valley, Piedmont, and Allegheny Plateau

How to identify it:

• Leaves with 7–9 rounded (not pointed) lobes and deep, rounded sinuses — lobes without bristle tips
• Light gray, scaly bark that often appears whitish or pale gray at a distance
• Rounded, oblong acorns 0.5–1 inch enclosed one-quarter in a warty, gray cup
• Wide-spreading crown with large, horizontal limbs on old-growth trees

Black Walnut (Juglans nigra)

Black walnut grows to its finest development in Pennsylvania's rich agricultural valleys — particularly in Lancaster, Chester, and York counties — where the deep, well-drained alluvial soils of the Piedmont produce specimen trees with massive, straight trunks of the highest-value timber in eastern North America. Pennsylvania has historically been a center of black walnut timber production, and the premium furniture and gunstock wood commands prices exceeding $10,000 for a single high-quality log from a mature tree. The chemical juglone, exuded from roots and leaf litter, suppresses many competing plants — a phenomenon called allelopathy — creating distinctive sparse understories beneath walnut trees that observant naturalists learn to recognize. The large, round nuts in a thick, pungent-smelling green husk ripen in October and are gathered for their rich, distinctive-flavored kernels.

Where to find it: Rich, moist, well-drained bottomlands, stream terraces, and lower slopes in the Piedmont, Ridge and Valley valleys, and agricultural lowlands statewide

How to identify it:

• Large pinnately compound leaves with 15–23 lance-shaped, finely toothed leaflets; terminal leaflet often absent or smallest
• Round, green, non-splitting husked nuts 1.5–2.5 inches in diameter with a pungent, iodine-like odor when crushed
• Dark, deeply furrowed bark with rough, diamond-shaped ridges on mature trees
• Chambered pith visible in cross-section of cut twigs — a reliable diagnostic feature

Chestnut Oak (Quercus montana)

Chestnut oak is the dominant tree of Pennsylvania's dry, rocky Appalachian ridges — the signature oak of the central and north-central ridge and valley topography where shallow, acidic, chert-and-sandstone soils preclude the richer-site oaks. From the Kittatinny Ridge and Blue Mountain in the south to the Allegheny Front and northern tier ridges, chestnut oak forms extensive forests that are critical habitat for breeding neotropical migrants including worm-eating warbler and black-and-white warbler. Its very thick, deeply ridged, dark bark is the thickest of any eastern oak relative to tree diameter and was historically the most commercially important source of oak tannin for the leather industry — Pennsylvania's tanning industry once stripped chestnut oak bark from millions of trees across the state. The large, round, sweet acorns are a major food source for deer and bears on Pennsylvania's ridges.

Where to find it: Dry, rocky ridges, chert and sandstone outcrops, and xeric slopes throughout the Ridge and Valley and Allegheny Plateau

How to identify it:

• Large, oval leaves 4–9 inches long with rounded, wavy teeth resembling chestnut leaves — not lobed like most oaks
• Exceptionally thick, deeply ridged, nearly black bark with massive, blocky ridges
• Large, oval acorns 1–1.5 inches, the largest of Pennsylvania's native oaks, enclosed halfway in a thick-scaled cup
• Often multiple trunks or a low, branching form on rocky ridge-top sites

Sugar Maple (Acer saccharum)

Sugar maple is a dominant hardwood in Pennsylvania's northern tier and the Allegheny Plateau, where it forms the classic northern hardwood forest alongside American beech and yellow birch — the same forest type that defines the Adirondacks and New England. In the Pocono Mountains, Endless Mountains, and northern counties, sugar maples produce reliable maple syrup; Pennsylvania ranks among the mid-Atlantic states' leaders in maple syrup production. Fall color from Pennsylvania's sugar maples peaks in mid-October in the northern counties, and popular destinations like the Endless Mountains Heritage Region and the Cherry Springs area draw leaf-peepers to witness the brilliant orange and red display. Sugar maples require cooler summers and more consistent moisture than the central and southern Pennsylvania climate easily provides, which limits their abundance south of a line roughly following Interstate 80.

Where to find it: Cool, moist upland forests in the northern tier, Pocono Mountains, and Allegheny Plateau above 1,500 feet

How to identify it:

• Classic 5-lobed maple leaf with U-shaped sinuses between pointed lobes, 3–6 inches wide
• Clear, watery sap from broken petiole (unlike Norway maple's milky white sap)
• Deeply furrowed, gray bark with irregular, shaggy-plated ridges on mature trees
• Opposite branch arrangement and paired samaras with wings at 60–90 degree angle

Sycamore (Platanus occidentalis)

The American sycamore is Pennsylvania's most massive native tree by girth — the Buttonwood Farm sycamore in Berks County and other champion trees in the Delaware and Susquehanna valleys regularly produce trunks of 10 to 15 feet in diameter, making them the stoutest trees in the eastern United States. Sycamores dominate the floodplain forests and river islands of every major Pennsylvania river system — the Delaware, Susquehanna, Schuylkill, Lehigh, and Allegheny — where their tolerance of periodic flooding and root saturation gives them an unmatched competitive advantage. The ghostly white upper bark, revealed as the brown outer bark exfoliates in patches, is visible from great distances along Pennsylvania's river valleys and is the most reliable identification feature at any time of year. Sycamore is a keystone of Pennsylvania's riparian ecosystems, and the hollow trunks of old trees provide nesting sites for chimney swifts, wood ducks, and barred owls.

Where to find it: Floodplain forests, river banks, stream terraces, and riparian corridors throughout Pennsylvania's major river systems

How to identify it:

• Ghostly white, cream, and tan upper bark revealed by exfoliating brown outer bark in irregular patches
• Massive, broadly lobed leaves 5–10 inches across resembling a maple but with alternately arranged stems
• Round, brown seed balls 1–1.5 inches hanging singly on long stalks, persisting through winter
• Massive trunk diameter — often the most expansive trunk of any tree in its riparian habitat

Sassafras (Sassafras albidum)

Sassafras is one of Pennsylvania's most distinctive and easily identified trees, famous for producing three different leaf shapes on the same tree — mitten-shaped with one lobe, mittens with two lobes (bilobed), and unlobed oval — a feature unique among Pennsylvania's native trees and a perennial source of delight for beginner naturalists. It is a common pioneer species in Pennsylvania's old fields, forest edges, and disturbed upland forests throughout the state, spreading prolifically by root sprouts to form dense clonal thickets. The roots, bark, and crushed leaves produce a distinctive root-beer or sassafras-tea fragrance, and the oil was historically used to flavor root beer before being restricted by the FDA. Blue-black, pea-sized fruits on bright red stalks ripen in September and are eagerly consumed by migratory thrushes, scarlet tanagers, and catbirds.

Where to find it: Old fields, forest edges, disturbed upland slopes, and early successional forests throughout Pennsylvania at lower elevations

How to identify it:

• Three distinct leaf shapes on the same tree: unlobed oval, single-lobed mitten, and 2-lobed mitten or trident
• Distinctive root beer / anise fragrance from crushed leaves, twigs, and especially roots
• Deeply ridged, orange-brown bark on mature trees, corky and aromatic
• Blue-black, oval fruits on bright red, club-shaped stalks in September

Tree of Heaven

Tree of heaven (Ailanthus altissima) is Pennsylvania's most widespread invasive tree, dominating roadsides, railroad rights-of-way, abandoned industrial sites, forest edges, and riparian corridors across the entire state from Philadelphia to Pittsburgh. Pennsylvania is the epicenter of the spotted lanternfly (Lycorma delicatula) invasion in the United States — the pest was first detected in Berks County in 2014 — and tree of heaven is its preferred host plant and overwintering site, meaning that tree of heaven management is now directly linked to spotted lanternfly control. The tree's ability to resprout from roots following mechanical removal makes it extraordinarily difficult to eliminate, and basal bark herbicide treatment is the most effective long-term control strategy.

Norway Maple

Norway maple (Acer platanoides) is a persistent invader of Pennsylvania's urban and suburban forest edges, creek corridors, and natural areas, spreading from its widespread use as a street tree throughout the Philadelphia, Pittsburgh, and Lehigh Valley metro areas into natural forest understories where it outcompetes native sugar maple seedlings. Its higher shade tolerance relative to sugar maple allows it to establish in fully closed-canopy forests, and it leafs out earlier and retains leaves longer than native maples, further suppressing native understory plants. Pennsylvania's parks and natural areas in the southeastern counties show significant Norway maple naturalization, and it is now found in forest understories as far north as the Pocono Mountains.

Autumn Olive

While primarily a shrub, autumn olive (Elaeagnus umbellata) commonly reaches small tree stature (15–20 feet) in Pennsylvania's old fields, forest edges, and disturbed areas across the state, where it was widely planted by the USDA for wildlife food and erosion control from the 1950s through the 1980s. It fixes atmospheric nitrogen, altering soil chemistry in ways that disadvantage native plants adapted to lower-fertility conditions, and each plant produces thousands of red berries that are widely dispersed by birds. It is particularly problematic in the Ridge and Valley barrens, shale barrens, and old field communities of central Pennsylvania, where it converts native grassland and early-successional shrub habitat to dense multi-stemmed thickets.

What is the significance of the American chestnut in Pennsylvania's forest history?

The American chestnut (Castanea dentata) was once the dominant canopy tree across Pennsylvania's ridges and slopes — some estimates suggest one in every four trees in the state was a chestnut before chestnut blight (Cryphonectria parasitica), introduced around 1904, killed virtually every mature chestnut in North America within 50 years. Pennsylvania's forests were fundamentally transformed by this loss, with oaks and red maple expanding to fill the chestnut's ecological role, but the dense mast crop and superior timber quality of chestnut have never been replaced. The American Chestnut Foundation, with significant programs in Pennsylvania, is developing blight-resistant hybrid chestnuts through backcross breeding and biotechnology, with restoration plantings beginning in Pennsylvania state forests.

Why is the hemlock woolly adelgid such a serious threat to Pennsylvania's forests?

The hemlock woolly adelgid (Adelges tsugae) is a tiny, aphid-like insect from Asia that kills eastern hemlock trees by inserting a stylet into the base of needles and extracting stored starches, causing needles to desiccate and drop within 1–4 years. Eastern hemlock has no natural resistance to the adelgid and no effective native predators, so untreated trees die rapidly. Pennsylvania has lost hundreds of thousands of acres of hemlock forest since the adelgid arrived in the 1980s, with severe consequences for cold-water stream temperatures, brook trout populations, and forest-interior bird communities that depend on hemlock's year-round shade and structure.

What is Pennsylvania's most commercially valuable native timber tree?

Black walnut (Juglans nigra) is consistently the most valuable timber tree per board foot in Pennsylvania, with premium veneer-quality logs selling for $10,000 or more. Its combination of rich chocolate-brown color, fine grain, stability, and workability makes it irreplaceable for furniture, gunstocks, and veneer. Black cherry (Prunus serotina) rivals walnut in value on the Allegheny Plateau, where the deep sandy soils of north-central Pennsylvania produce the straightest, highest-quality cherry timber in the world — the 'Allegheny cherry' commands a significant premium in the global hardwood market. Pennsylvania leads the nation in black cherry timber production.