Delaware Wildflowers • Guides

Persicaria — Tearthumb, Smartweed
14 species in Delaware. These were called Polygonum until recently. These plants all have jointed stems, with a sheaths around the nodes where the leaves join the stem. The characteristics of these sheaths are important to identifying the species.
Three are vines with prickly stems

Persicaria perfoliata, Mile-a-minute (Polygonum perfoliatum)
Invasive non-native, Piedmont & coastal plain
The sheath forms a leaf-like blade around the stem. Fruit is bright blue.

Persicaria sagittata, Arrowleaf Tearthumb (Polygonum sagittatum)
Native, Piedmont & coastal plain
Larger leaves are shaped like a long narrow arrowhead, with small lobes at the base that point towards the stem.

Persicaria arifolia, Triangle-leaf Tearthumb (Polygonum arifolium)
Native, Piedmont & coastal plain
Larger leaves are more triangular, with lobes that point to the sides. Also called "Halberd-leaved tearthumb."

Eleven are not vines

Four species have sheaths without bristles (though they may be hairy.)

Two species grow in water or wet soil.

Persicaria amphibia, Water Smartweed (Polygonum coccineum)
Native, coastal plain only
Pink flowers in 1 - 3 terminal spikes.

Persicaria glabra, Dense-flowered Smartweed (Polygonum densiflorum)
Native, coastal plain only
Whitish flowers in a panicle of several spikes.

Two species grow in drier areas.

Persicaria pensylvanica, Pennsylvania Smartweed (Polygonum pensylvanicum)
Native, Piedmont & coastal plain
The upper stem is covered with stalked glands — short hairs ending in tiny knobs.

Persicaria lapathifolia, Dock-leaf Smartweed (Polygonum lapathifolium)
Native, Piedmont & coastal plain
The upper stem is smooth or with stalkless glands.

Seven have sheaths with bristles

In one species, the tip of the sheath spreads, a "horizontal flange"

Persicaria orientalis, Prince's-plume Smartweed (Polygonum orientale)
Non-native, Piedmont only
Broad leaves, compared to most of the Persicaria species, and dark pink or red flowers.

In six, the tip of the sheath does not spread

Two species have tiny dots on the mature flowers

Persicaria hydropiper, Marshpepper Smartweed (Polygonum hydropiper)
Non-native, Piedmont & coastal plain
Stems reddish, sheaths swollen on one side.

Persicaria punctata, Dotted Smartweed (Polygonum punctatum)
Native, Piedmont & coastal plain
Stems green, sheaths not swollen one side.

Four don't have dotted flowers

Persicaria maculosa, Lady's Thumb Smartweed (Polygonum persicaria)
Non-native, Piedmont & coastal plain
Pink-purple flowers in a dense inflorescense up to 1/2" diameter. Leaves often have a dark blotch, but other species sometimes have this too.

Persicaria hydropiperoides, Water-pepper Smartweed (Polygonum hydropiperoides)
Native, Piedmont & coastal plain
Pink-purple flowers, inflorescense less dense, under 1/4" diameter. Perennial, wet places.

Persicaria longiseta, Longbristle Smartweed (Polygonum cespitosum)
Invasive non-native, Piedmont & coastal plain
Pink-purple flowers, bristles as long as the sheath or longer.

Persicaria virginiana, Virginia Smartweed (Polygonum virginianum, Tovara virginiana)
Native, Piedmont & coastal plain
White flowers in a loose inflorescense.

One species on the checklist is no longer found in Delaware.

Persicaria careyi, Carey's Smartweed (Polygonum careyi)
Historical native, coastal plain only

Sources: The Flora of Delaware, Herbaceous Plants of Maryland.

Copyright David G. Smith

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