Know Your Natives – Cream Wild Indigo

Cream wild indigo (Baptisia bracteata*), of the Pea (Fabaceae) family occurs from the Midwest to Texas and the Southeastern states except for Florida.  It is also reported from Connecticut and New Jersey.  In Arkansas, it occurs mostly statewide except for some portions of the Mississippi Alluvial Plain.  Another common name is long-bract wild indigo.  The genus name is derived from Greek for “to dye”, based on some plants of the genus having been used to produce a blue dye similar to that from the true “indigo” plants (Indigofera spp.).  The specific epithet, from Latin, relates to the large bracts subtending the flowers.

Cream wild indigo is a long lived herbaceous perennial that is found in various mesic to dry soils in the full sun of prairies to partial shade of open woods and savannahs.  Reaching a height of about 2 feet with a wider width, it has one or multiple stems from an impressively large rootstock.  Being a legume, the plant pulls nitrogen from the air into its roots with the aid of bacteria.

In spring, terete (round) stems have a heavy pubescence of uniformly short, white hairs.  These hairs cast a grey tinge to purple stems and create a white halo at stem edges.  Bracts along stems and branches occur singly or in pairs.  (Paired bracts occurring with the leaves are technically stipules.)  The lowest single bract at or below ground level is sessile and tightly clasps the stem.  Next up-stem, the upper portion of a single clasping sessile bract flares outward.  Thereafter up-stem, outward growing pairs of bracts subtend two straight branches that diverge one from the other at 45 or more degrees with one branch noticeably smaller than the other.  The larger branch emerges from the center of the bract pair while the smaller branch emerges to one side between the bracts.  Up-stem, smaller and larger branches switch from one side to the other, resulting in zigzag stems.  For those branches that terminate with a leaf (instead of an inflorescence–see below), only one “branch” is present near the top of the plant, but each leaf is still subtended by a pair of stipules.  Bracts and stipules are a greyish-green color.  Bracts are broadly lanceolate with the lower single bracts being more broad to triangular.  Paired stipules are longer and more widely spaced lower on the plant with length and spacing decreasing up-stem.  On branches that produce inflorescences, the inflorescence itself is subtended by a pair of bracts which also subtends a smaller branch.

Cream Wild Indigo - Baptisia bracteataPhoto 1:  Single bracts occur lower on pubescent stems.  Pairs of bracts subtend a smaller branch and larger branch.  Imbricated floral bracts can be seen at top.

Leaves, greyish-green on upper and lower surfaces, are pubescent on upper surfaces and less so on lower surfaces.  Leaves are trifoliate with leaflets that are 1 to 3 inches long and 1/2 to 1 inch wide.  Leaves have a terminal leaflet and two lateral leaflets typically set almost perpendicular to the terminal leaflet.  Leaflets are oblanceolate and smooth margined (entire) with the central leaflet typically being broader.  With stipules varying from 1/4 to 1-1/2 inches long, some leaves may appear to have five leaflets.   Leaf size decreases up-stem.  Leaflets do not have petiolules (individual leaflet stalks).  Leaves are typically sessile, although some plants have petioles over an inch long.  Leaflets, with pinnate venation, have gradually tapered bases and tapered, more rounded tips.

The inflorescence becomes evident on tips of branches shortly after new spring growth appears.   Inflorescences first appear as stubby, elongated and rounded clusters covered with imbricated (overlapping) floral bracts.  As the inflorescence lengthens, its raceme-type structure (each flower on separate pedicel) becomes more apparent and its pea-type flower buds emerge.  Flowers are subtended by single, broadly lanceolate and entire floral bracts (which had previously overlapped each other).   Floral bracts, pedicels and peduncles have coloration and pubescence similar to stems and branches.  At full bloom, racemes may be twelve or more inches long with flowers in loose or dense formation.  Overall stem structure of plant along with weight of flowers causes racemes to be oriented horizontally, close to or on the ground.

Cream Wild Indigo - Baptisia bracteataPhoto 2:   With growth of raceme, previously imbricated floral bracts spread outward and calyxes open.  Inflorescence grows on the larger of branch pairs.

With anthesis (full bloom) in mid-April, buds positioned to the side or below the level of the peduncle (stalk of raceme) shift to face upward, and calyx tubes become green and less pubescent.  Up to 30 or more inch-long flowers are borne on inch-long pedicels.  Calyx tubes (formed by fused sepals) have four triangular tips.  Flowers are pea-like with a flared upright petal (banner or standard) with a cleft at mid-petal and a pair of forward projecting petals (wings) which enclose a pair of smaller petals (keel).  The keel, visible when flower is viewed from below, encloses ten separated stamens with white filaments and brown anthers as well as  a pistil with a white style and yellow stigma.  A greenish elongate ovary is located at the base of the white style (superior ovary).  Exposed surface of all petals is a similar light yellow or “cream” color.  Bracts, calyxes, peduncles and pedicels have color and pubescence  similar to that of  the stems and branches.

Cream Wild Indigo - Baptisia bracteataPhoto 3:  Only one raceme was produced on this plant with other branches terminating with leaves.  Photo taken in mid-April

Cream Wild Indigo - Baptisia bracteataPhoto 4:  Inner petals (keel) can be seen in mature flowers on right.   Note prescence of single floral bracts and pubescence.

Fertilized flowers are followed by light green seed pods, 1 to 2 inches long, that appear to be inflated.   Pod bases and beaks are greatly constricted in comparison to overall pod.  The pod beak (the remnants of the style) is exaggerated.  Calyxes are persistent.  A row of yellowish-green, bean-like 1/8 inch seeds on both sides of pod’s hinge-line occupies only a small portion of  the space available in pods.   Pods become black with maturity while leaves are still green.  With freezing temperatures, stems/branches become blackened and break-off at ground level.  The dead plant, with pods attached, is blown about tumble-weed fashion so that the eight to twenty seeds per pod are dispersed.

Cream Wild Indigo - Baptisia bracteataPhoto 5:  In late June, pubescence has been reduced.   Entire length of style persists on the seed pod as a “beak”.  Calyxes and floral bracts remain.

Cream Wild Indigo - Baptisia bracteataPhoto 6:  In mid July, seed pods mature.  Leaves shown are on a terminal branch where paired stipules are present, but only one branch continues in zigzag fashion.

In a garden or natural area, cream wild indigo is a long-lasting perennial of modest compact size that is adaptable to various soils and does well in full sun or partial shade.  It has an interesting structure and striking flower clusters followed by showy seed pods.  Stems blow away in winter for a fresh start in spring.   Newly germinated plants require about three years to bloom.  Flowering is better on drier more sunny sites.

 

*Several varieties of cream wild indigo have been identified. The only variety reported in Arkansas is Baptisia bracteata var. leucophaea (which has sometimes been treated at the species level as B. leucophaea).

Other native species of the genus in Arkansas are:

  • white wild indigo (Baptisia alba var. macrophylla)
  • blue wild indigo (Baptisia australis var. minor)
  • Nuttall’s wild indigo (Baptisia nuttalliana)
  • yellow wild indigo (Baptisia sphaerocarpa).

Some natural hybrids of these are also known.

Article and photographs by ANPS member Sid Vogelpohl

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