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// SPECIES PROFILE · PERENNIAL · NATIVE · HUMMINGBIRD-COEVOLVED

Cardinal Flower

Lobelia cardinalis

The most intense pure red of any North American native perennial, blazing from August spires that rise from the shaded seeps and creek banks of the NE Oklahoma Ozarks and the Cross Timbers bottomlands. Lobelia cardinalis has effectively co-evolved with the ruby-throated hummingbird — its long curved scarlet corolla, its lack of fragrance, and its near-zero accessibility to bees are all hallmarks of an ornithophilous (bird-pollinated) flower. Where you find a wild cardinal flower in eastern OK in late summer, you will almost always find a hummingbird working it within minutes. It is a short-lived perennial that needs consistently moist soil and reliably reseeds itself in suitable conditions; given the right wet, dappled spot in a Tulsa garden, it will return year after year.

// QUICK FACTS
Family
Campanulaceae (subfamily Lobelioideae)
Group
Short-lived herbaceous perennial
Native range
SE Canada → N South America; throughout E OK along streams & seeps
USDA hardiness
Zones 3–9 (Tulsa = 7a/7b)
Mature size
2–4 ft tall · 1–2 ft wide
Bloom
Late July–September (peak August in Tulsa)
Flower
Two-lipped, tubular, 1–1.5 in, vivid scarlet
Lifespan
3–5 yrs per crown; persists by self-seeding
Sun
Part shade ideal · full sun only with constantly wet soil
Soil
Consistently moist to wet; tolerates seasonal flooding
Water
Wetland indicator FACW; never let the crown dry out in summer
Pollinator
Almost exclusively ruby-throated hummingbird; some sphinx moths
Toxicity
All parts toxic if ingested in quantity (lobeline alkaloids)
Deer
Rarely browsed (alkaloid-bitter)
Ecological role
Hummingbird nectar specialist · wet-shade native
Cardinal Flower (Lobelia cardinalis) — vivid scarlet two-lipped bloom on a tall spike
Lobelia cardinalis — the diagnostic pure scarlet, two-lipped, hummingbird-shaped corolla on a tall spike. Photo via Wikipedia / Wikimedia Commons.

Identification

[ field key — basal rosette · spike · scarlet corolla · wet site ]

Habit & rosette

A clump-forming herbaceous perennial with a tight basal rosette of dark green, lance-shaped, slightly toothed leaves, from which a single (occasionally branched) erect flowering stem rises in late summer. The basal rosette persists more or less evergreen through mild winters in Tulsa — a useful winter ID. Roots are fibrous and shallow; the plant does not have any drought-storage organ, which is exactly why moisture matters so much.

Stem leaves

Stem leaves are alternate, lance-shaped to elliptic, 2–6 in long, with finely toothed (serrate) margins and short petioles or sessile bases. Dark green, sometimes bronze-tinged, lightly hairy or smooth. Leaves grade smaller as they ascend the flowering stem and become bract-like in the inflorescence.

Flowers — the diagnostic spike

Inflorescence is an unbranched terminal raceme 6–18 in long bearing 30 to 60 flowers, opening sequentially from the bottom up over 3–5 weeks (late July through September in Tulsa). Each flower is two-lipped: three spreading lobes form the lower "lip" and two recurved lobes the upper, with the stamens fused into a column that arches over the lower lip and presents pollen precisely against a hovering hummingbird's forehead. Color is the famous pure cardinal-red scarlet — one of the few perennials with no orange or pink overtones at all.

The flower is protandrous (male first, then female): each flower presents pollen for 2–3 days and then exposes its receptive stigma, an evolutionary trick that promotes outcrossing as a hummingbird works up an inflorescence.

Confusables

Almost unmistakable in flower — no other native eastern OK perennial combines a tall scarlet spike with two-lipped tubular flowers on a wet-shade site. Out of flower, the basal rosette resembles Lobelia siphilitica (great blue lobelia, wet-meadow native, blue flowers in late summer), Lobelia inflata (Indian tobacco, dry woods, weedy), and a number of evening-primrose rosettes — if in doubt, wait for bloom. The cultivated standing cypress (Ipomopsis rubra) is also red but has feathery dissected leaves and a Phlox-family habit.

Habitat & Range in NE Oklahoma

Lobelia cardinalis ranges from southeastern Canada through the eastern US and south to Colombia, with a near-continuous distribution east of the Great Plains. In Oklahoma it is essentially confined to the moist forests, stream margins, and seep-fed slopes of the eastern third of the state — the Ouachita Mountains of LeFlore and Pushmataha Counties, the Ozark uplift of Adair, Cherokee, and Delaware Counties, and the shaded creek bottoms of the Cross Timbers transition zone. Wild stands in the Tulsa region occur along Bird Creek tributaries, the Illinois River corridor, spring-fed seeps in the Ozark foothills around Tahlequah, and the shaded riparian shelves of the Caney and Verdigris.

Cardinal flower is a wetland-indicator (FACW) species and classic edaphic specialist — it is present where the water table stays at or near the surface, and absent or briefly transient where it does not. The microhabitats it occupies in NE Oklahoma share three things: moist mineral soil at all times, dappled or part shade from an overstory of sycamore, river birch, american hornbeam, or sweetgum, and a break in the herbaceous canopy — a creek bank, the gravel margin of a flood scour, a recently disturbed seep face — that prevents grass and sedge competition from outcompeting the rosette during establishment. This combination is rare enough in unmanaged landscapes that wild cardinal flower is locally uncommon and worth recording wherever you find it.

In a residential Tulsa landscape the species is fully growable but requires the same combination: a rain-garden basin, a constantly moist shaded bed, the north side of a downspout splash block, or the edge of a small ornamental pond. In full-sun gardens with normal irrigation, it will bloom once and then die in the following summer; the failure mode is almost always summer crown desiccation, not winter cold.

Ecology & Wildlife Value

[ hummingbird coevolution · sphinx moths · conservation · toxicity ]

Ruby-throated hummingbird

Cardinal flower is one of the textbook examples of ornithophily in eastern North America. The corolla is too long for most native bees and most butterflies to reach the nectar, and the column of fused stamens and stigma is positioned exactly to deposit pollen on the forehead of a hovering hummingbird. In NE Oklahoma that hummingbird is almost exclusively the ruby-throated hummingbird (Archilochus colubris), which is in active fall migration through the region during cardinal flower's August–September bloom — the timing is not coincidental.

Other visitors

Sphinx moths (notably the hummingbird clearwing, Hemaris thysbe) and a few large swallowtails — especially the eastern tiger swallowtail — also work cardinal flower for nectar, with the swallowtails using their long tongues to bypass the corolla geometry. Butterflies are not particularly effective pollinators because their bodies do not contact the stamen column the way a hummingbird's forehead does. Halictid sweat bees occasionally rob nectar from holes chewed at the corolla base.

Larval & insect food web

Cardinal flower is a known larval host for the pink-washed looper moth and a small number of other specialist Lepidoptera that have evolved tolerance for the toxic lobeline alkaloids. The seed is extremely small and dust-like (the entire genus Lobelia has miniature dust seeds) — few birds eat them directly; primary dispersal is by water flow.

Conservation status

Globally secure (G5) but locally declining in the southern Plains as riparian seeps are drained, channelized, or shaded out by invasive privet and bush honeysuckle. Cardinal flower is a useful indicator of intact riparian seep habitat — where it persists, the rest of the spring-seep flora is usually intact too. The species is included in the Oklahoma Native Plant Society's regional pollinator-plant lists for hummingbird gardens.

Toxicity: All parts of cardinal flower are toxic if eaten in quantity. The plant contains the pyridine alkaloid lobeline and related compounds — bitter, emetic, and at high doses cardiotoxic. There is a traditional medicinal use record (see below) but the safety margin is narrow and modern self-medication is strongly discouraged. The bitterness keeps deer and rabbits off the plant, which is one of the few unalloyed advantages it offers the gardener.
For the hummingbird garden: Combine cardinal flower with great blue lobelia (L. siphilitica, same wet-shade habitat, blue flowers, also blooms August–September), crossvine, buttonbush, and a stand of wild bergamot on the drier perimeter. A patch of 5–10 cardinal flower plants in a shaded rain garden will draw hummingbirds reliably through the entire fall migration window.

Horticulture & Care

[ siting · planting · reseeding · cultivars · failure modes ]

When to plant intentionally

Cardinal flower is the right plant when you have a consistently moist, partly shaded location and a hummingbird goal. The single best site in most Tulsa-region yards is the bottom of a downspout-fed rain garden basin under a small ornamental tree or the dappled north side of a house. Use it in woodland-edge gardens, beside a small pond or fountain, in a constructed bioretention cell, or massed in a shaded riparian restoration project. Avoid full-sun perennial borders, traditional lawn-edge beds, and any site where summer irrigation is intermittent.

Planting & establishment

Maintenance & reseeding

Cardinal flower is naturally short-lived — individual crowns persist 3–5 years and then fade out. The trick to keeping a stand long-term is to let it self-seed: leave seed heads intact through fall, do not mulch heavily over the soil surface, and accept some volunteer seedlings appearing 1–3 ft from the parent plant. After the first hard frost, cut spent flowering stems to 6", but leave the basal rosettes untouched — they overwinter green and need light. A 5-plant initial installation in a good site will commonly become a self-sustaining drift of 15–30 plants within three years.

Common failure modes

Notable cultivars & selections

Cultivar / variety Habit Distinguishing feature Notes for Tulsa
Straight species 2–4 ft Pure scarlet; full ecological function; reliable reseeder The recommended choice for hummingbird gardens and restoration plantings.
'Black Truffle' 2–3 ft Dark bronze-purple foliage with red flowers; striking contrast Performs comparably to the species in good wet shade; popular at regional retail.
'Queen Victoria' 2–3 ft Deep red-bronze foliage, intense scarlet flowers Handsome but tends to be shorter-lived than the species; treat as a biennial in marginal sites.
'Fried Green Tomatoes' 2–3 ft Green foliage, vivid red bloom; selected for vigor One of the most reliable commercial selections for southern gardens.
Lobelia × speciosa hybrids ('Starship Scarlet', 'Vulcan Red') Variable, often shorter Hybrids of L. cardinalis, L. siphilitica, and L. fulgens; broader color range Treat as annuals or short-lived perennials in Tulsa; less hardy and less ecologically functional than the species.
White / pink forms (L. cardinalis 'Alba', 'Rose Beacon') 2–3 ft White or pink-flowered selections of the species Lose the diagnostic scarlet (and most of the hummingbird visitation); choose for novelty only.

For ecological function, choose the straight species or 'Black Truffle' — the more "improved" hybrid lines lose hardiness, longevity, or hummingbird visitation in proportion to how far they have been bred from the wild type.

Cultural & Material Uses

Cardinal flower is primarily an ornamental and ecological plant rather than a material one, but it has a notable Indigenous medicinal record and a long history in horticulture.

Sources & Further Reading

  • USDA NRCS PLANTS Database — Lobelia cardinalis: plants.usda.gov/plant-profile/LOCA2
  • USDA Forest Service Fire Effects Information System (FEIS) — Lobelia cardinalis: fs.usda.gov/database/feis/plants/forb/lobcar
  • Oklahoma Native Plant Society — native pollinator and hummingbird plant lists for the eastern Oklahoma region.
  • Oklahoma State University Extension — Native Plants for Oklahoma Landscapes and OSU Horticulture rain-garden bulletins.
  • Lady Bird Johnson Wildflower Center — Native Plant Database, Lobelia cardinalis: wildflower.org — LOCA2
  • Missouri Botanical Garden Plant Finder — Lobelia cardinalis cultivar profiles.
  • Bertin, R.I. (1982), "The ecology of sex expression in red buckeye and other hummingbird-pollinated plants", Ecology 63: 445–456 — on coevolution of ruby-throated hummingbirds and eastern red flowers.
  • Brown, B.J. & Mitchell, R.J. (2001), "Competition for pollination: effects of pollen of an invasive plant on seed set of a native congener", on Lobelia pollination biology.
  • Moerman, D.E. (1998), Native American Ethnobotany, Timber Press — documented Indigenous medicinal uses of Lobelia cardinalis by tribe.
  • USFWS National Wetland Plant List — wetland indicator status (FACW) by region for Lobelia cardinalis.
  • Wikipedia — Lobelia cardinalis: en.wikipedia.org/wiki/Lobelia_cardinalis (CC BY-SA 4.0; portions of the description and ethnobotany sections summarize Wikipedia content).
  • Tyler, V.E. (1993), The Honest Herbal — cautionary review of lobeline pharmacology and historical medicinal use of Lobelia spp.

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Companion Planting

[ guild · polyculture · cross-layer pairings ]

Along a stream or seasonal floodplain, cardinal flower pairs naturally with: american hornbeam (Carpinus caroliniana), american elderberry (Sambucus canadensis), crossvine (Bignonia capreolata), inland sea oats (Chasmanthium latifolium), maidenhair fern (Adiantum pedatum), and black tupelo (Nyssa sylvatica).

Combine cardinal flower with the warm-season grasses listed above for a self-sustaining matrix.