Know Your Natives – Downy Lobelia

Downy Lobelia (Lobelia puberula) of the Bellflower (Campanulaceae) family is a pubescent, herbaceous perennial bearing showy racemes of blue to lavender flowers. The genus name recognizes Matthias de l’Obel, a Flemish 16th-century physician and botanist who is credited with being the first to attempt to classify plants by attributes other than their medicinal uses. The specific epithet is the diminutive of the Latin puber, downy. In the U.S., Downy Lobelia occurs in a northeast-trending swath from eastern Texas and Oklahoma to the Atlantic Coast. In Arkansas, the species occurs across most of the state except for the northernmost counties and eastern portion of the Mississippi Alluvial Plain. Habitats vary from sunny to partially shaded bottomlands and mesic uplands: deciduous and pine woodlands, forest borders, meadows, ditches, and rights-of-way.

In early spring, an erect stem grows from the fibrous-rooted crown, the diameter of the root crown only slightly larger than that of the stem. Stems are slender, pale green to reddish, to ⅛ inch at base, growing to 3 feet tall. They are unbranched (unless their tips are damaged) and covered with dense, short, soft pubescence. Dry, naked stems may persist into the next growth-year.

Photo 1: A new stem grows from the crown of the stubby, erect, elongated main root. Photo – July 14
Photo 2: When damaged, several axillary stems may develop below the damage. Stems are densely pubescent. Photo – September 19.

Alternate simple stem leaves decrease in size upwards into the racemose inflorescence where they become floral bracts. Leaf shape varies: from ovate to elliptic and oblanceolate below the raceme, triangular to short-lanceolate within the raceme. Leaves are narrowed to short-petiolate, sessile or even clasping bases. Leaf margins vary from entire to finely and even coarsely serrate with sharp (mucronate) tips. Tips of leaves and bracts may bear white calluses due to transpiration of the plant’s white sap. Dense pubescence of leaf surfaces is similar to that of stems. Pinnate venation is obscure on the upper surface, but well expressed on the lower surface. Midribs of both surfaces are raised. Largest leaves may be 4+ inches long and 1½+ inches wide.

Photo 3: Dense pubescence covers the stem and upper and lower leaf surfaces. The crinkled leaf margins are not ciliate, but become highlighted in red in more sunny settings. Leaf-size diminishes upwards.
Photo 4: These sessile leaves, from a single stem, vary from ovate to broadly triangular to lanceolate and bear entire to slightly serrate margins. Upper surface displayed on left, lower surface right. Pinnate veins are obscure on upper surface. Photo – September 19.
Photo 5: These sessile leaves, from a single stem, are oblanceolate to deltoid with margins that have fine to coarse serrations. Upper surface displayed on left, lower surface right. Lower-left leaf is 2 inches long. Photo – October 17.

Blooming from late August into October, the inflorescence, along the upper third to half of the stems, is a raceme. Flowers in bloom are congested near the tip of the raceme but become spread out in fruit as the rachis elongates. Flowers are secund––aligned on the sunny side of the stems––and disposed spreading to ascending from the rachis on short, ascending pedicels, ⅛-¼ inch long. They are subtended by single bracts that decrease in size distally.

Photo 6: Developing flowers are amply spaced; flowers in bloom are congested near the tip of the inflorescence. Appearing to be sessile, flowers have short pedicels that hug the rachis.

Corolla morphology is complex and best understood from pictures rather than description. Suffice it to say that the showy, blue to lavender, tubular corollas are bilabiate, or 2-lipped. The upper lip is narrowly and deeply split into 2 lobes, the lower lip prominently 3-lobed, forming a landing pad for pollinating insects. Exterior of the entire corolla is uniformly pubescent, the interior glabrous.

Photo 7: Flowers are secund along the rachis. Central lobe of lower lip may be variably white. Note change of leaf size and shape along stem (below) and rachis (above). Photo – September 25.
Photo 8: The tubular flowers are 2-lipped. The upper lip is split, comprising 2 lanceolate lobes; the lower lip divides distally into 3 broad, spreading lobes.

Flowers, to about ¾ inch long, have 5 white to lavender stamens (filament + anther) that are disposed around the style and stigma––the ovary is inferior. The slightly pubescent filaments, standing free along most of their length, become fused near their tips where they bear elongate, pubescent, gray anthers that are also fused, into a ring. At early-anthesis, the style is surrounded by the filaments with the stigma enveloped by the anther ring. After pollen is shed, style growth protrudes the rounded stigmas beyond the ring, where the pollen is available to forgaging insects. The anther ring remains in the throat of the corolla.

Corollas are surrounded by a short calyx tube and 5 prominent, linear-lanceolate lobes. Calyx is medium green to reddish in sunny areas, with ciliate lobe margins. The inferior ovary is densely pubescent.

Photo 9: The knobby stigma becomes exserted while the anther ring remains within the throat (see flower at upper right-center). Note ciliate calyx lobes.
Photo 10: Calyx lobes are linear-lanceolate from a broad base. Lobe margins, with ciliate pubescence, are typically entire but may be serrated. (Photo taken down-rachis.)
Photo 11: Display shows 1) pale green receptacle with reddish calyx lobes, 2) pale green style with knobby stigma, 3) two lanceolate lobes of the upper lip, 4) lower lip with three broad lobes, and 5) filaments joined distally and topped with the anther ring.

After flowers fade, the shriveled brown corolla, stamens and style/stigmas remain attached at the summit of the ovary. The inferior ovary below the calyx enlarges into a conic capsule at maturity. Tightly packed ovules develop into minute, yellow-brown seeds. When the glabrous capsules dry, the tips of the 2 valves dehisce separately so that a pair of gaping pores appears, side-by-side. Dry capsules quickly disintegrate. Each capsule may produce hundreds of seeds. Surface of seeds is tuberculate. Seed dispersal is by wind and surface water.

Photo 12: Drying flower parts remain attached to developing capsules. The leathery calyx lobes hide and protect the capsule. These floral bracts have coarse serrations. Photo – October 17.
Photo 13: With calyx lobes and dry flower parts removed, the exterior of the developing capsules can be seen. The short pedicels (¼ inch long), hugging the rachis, have several appressed, tiny, linear bracteoles.
Photo 14: The conic capsules have axile placentas attached to a partition separating the 2 valves. This capsule is ¼ inch long and 3/16 inch wide. Ovoid seeds are tuberculate (see uppermost seed on left).
Photo 15: The apex (as shown) of this dry capsule (3/16 inch wide), having dehisced, has 2 gaping pores separated by the partition (see arrows). Seeds shown in inset photo are about a third of the seeds in this particular capsule. Squares = ¼ inch. Main Photo – October 14. Inset Photo – October 30

An additional 5 species of Lobelia occur in Arkansas: Pale Lobelia (L. appendiculata), Cardinal Flower (L. cardinalis), Indian Tobacco (L. inflata), Great Blue Lobelia (L. siphilitica), and Pale Spike Lobelia (L. spicata). Downy Lobelia is distinguished by its dense pubescence on stems, leaves/bracts, rachis, and exterior of corollas. Unlike the somewhat similar Great Blue Lobelia, flowers of the smaller Downy Lobelia are more loosely spaced and oriented to the sunny side of the raceme.

Downy Lobelia, although not especially eye-catching, should be welcomed in a natural area or practically any garden with mesic to wet soil and partial to full sun. It is a small, erect, non-aggressive herbaceous plant which can be attractive throughout the growing season. Plants in wet, sunny habitats are stouter with more flowers and healthier fruits. Great nectar sources for swallowtails and hummingbirds. May be grazed by deer.

Article and photographs by ANPS member Sid Vogelpohl

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