BORAGINACEAE (Borage Family)

Contributed by David J. Bogler and George Yatskievych

Plants annual, biennial, or perennial herbs (shrubs or trees elsewhere). Stems unbranched or branched, often hairy, sometimes appearing bristly, the hairs often with persistent pustular bases. Leaves alternate and sometimes also basal, well developed (except sometimes toward the stem base in Lithospermum and a few other genera), the margins entire. Stipules absent. Leaf blades simple, sessile or tapered to an often winged petiole, the surfaces usually stiffly hairy, the hairs often with persistent pustular bases (with calcified or silicified walls, known as cystoliths) and roughened to the touch, less commonly glabrous. Inflorescences mostly of terminal racemes or spikes, these often appearing coiled (scorpioid) and uncoiling as the flowers develop, sometimes panicles, seldom of solitary axillary flowers, the flowers most commonly subtended by bracts. Flowers actinomorphic (the corolla zygomorphic in Echium, the calyx zygomorphic in some Myosotis species), hypogynous, usually perfect; cleistogamous flowers sometimes present. Calyces usually deeply 5-lobed, the lobes equal or unequal, persistent and sometimes becoming enlarged at fruiting. Corollas (short and inconspicuous in cleistogamous flowers) usually shallowly 5-lobed, often trumpet-shaped, less commonly saucer-shaped, funnelform, narrowly bell-shaped, or tubular, the inside of the throat sometimes blocked by small appendages. Stamens usually 5, the filaments attached in the corolla tube, short or long, the anthers most commonly not exserted, rarely exserted, attached at their base, usually yellow. Pistil 1 per flower (but sometimes appearing as 2–4), of 2 fused carpels. Ovary usually deeply 4-lobed, usually 4-locular and with 1 ovule per locule, the placentation axile or sometimes appearing nearly basal. Style 1, usually attached in the pit between the ovary lobes, sometimes on a short, upward projection of the receptacle between the lobes, entire, usually not persistent at fruiting, the stigma sometimes 2-lobed, capitate or discoid. Fruits usually schizocarps splitting into (1–)4 nutlets, these 1-seeded, indehiscent, with a hardened, sometimes bony outer wall, less commonly a drupe with 4 (1-seeded) or 2 (2-seeded) stones. One hundred to 130 genera, about 2,500 species, nearly worldwide.

In the strict sense, the Boraginaceae are recognized by their alternate leaves, stiff hairs with pustular bases (cystoliths), tightly coiled scorpioid inflorescences, actinomorphic flowers, 4-lobed ovaries with a gynobasic style, and fruits consisting of 4 nutlets. Interestingly, gynobasic styles and nutlets apparently evolved independently in the Verbenaceae-Lamiaceae alliance (which usually have zygomorphic corollas). The Boraginaceae in the strict sense are related to a series of taxa variously recognized as subfamilies or separate families, including the Hydrophyllaceae, Heliotropiaceae, Cordiaceae, Ehretiaceae, Lennoaceae, and Wellstediaceae. The Hydrophyllaceae mostly share the distinctive scorpioid inflorescence and sometimes are combined into Boraginaceae, but they differ in having a capsular fruit and parietal placentation. They are treated as a separate family in the present work. Heliotropium is the only Missouri genus of Heliotropiaceae, a group of 3 genera that is distinguished by a terminal style, usually dry but drupaceous fruit, and the frequent presence of a stigmatic appendage. Ehretiaceae (11 genera, about 170 species) and Cordiaceae (3 genera, about 325 species), which some botanists combine under the former name, are mostly woody plants with divided styles and 2 stigmas in the former group and 4 stigmas in the latter group. They are most diverse in tropical and warm-temperate regions. The Cordiaceae do not occur in Missouri, but the introduced genus Tiquilia is here treated in the segregate family Ehretiaceae. The Lennoaceae (2 genera, 4 species) are a small group of succulent root parasites lacking chlorophyll and occur from the southwestern United States to northern South America. The small African genus Wellstedia Balf. f. (3 species) usually is treated as a subfamily of the Boraginaceae and is unique within the complex in its somewhat flattened capsular fruits.

The number of families to be recognized in this complex is still somewhat controversial. Molecular studies using ITS rDNA sequences and secondary structures (Gottschling et al., 2001) and ndhF sequence data (Ferguson, 1998) indicate these groups are indeed related and support the traditional classification, with Boraginaceae in the strict sense as the sister group to the other taxa. The decision to split the Boraginaceae into several related families that are easily separable morphologically avoids the problem of having to combine the Hydrophyllaceae into a broadly circumscribed concept of Boraginaceae. See the treatments of Ehretiaceae, Heliotropiaceae, and Hydrophyllaceae (the last two in the forthcoming Volume 3) for further discussion.

Although the Boraginaceae usually are easy to identify at the family level, the characters used to identify genera and species are rather technical and may require observation at relatively high magnification. The leaves provide only a few characters, differing mainly in size and shape. The flowers vary in size, shape, and color. Some genera have characteristic appendages or flaps of tissue (fornices, faucal appendages) inside the tube of the corolla or blocking the throat. The size and shape of these appendages are important characters but are difficult to observe, especially in pressed specimens. The length of the style relative to the anthers is also variable and sometimes an important character. Several genera of Boraginaceae are heterostylous, in which populations contain individuals with long styles (pin flowers) and other individuals with short styles (thrum flowers), relative to the position of the anthers. The insertion of the stamens is sometimes variable, and even the pollen is sometimes dimorphic. Fruits vary in the size and shape of the nutlets, how they are attached to the receptacle, and surface ornamentation. Mature fruits sometimes are needed to identify the species with confidence.

Members of this family are of relatively little economic importance, although many species are cultivated as ornamentals and a few species are used medicinally. Boraginaceae produce a variety of pyrrolizidine alkaloids and other chemical compounds that may be toxic or carcinogenic (Burrows and Tyrl, 2001). Livestock can be poisoned by eating the plants directly or as contaminants in their feed. The symptoms are cumulative and include loss of coordination, delirium, depression, and liver necrosis. The bark of the root in some species produces a purple napthaquinone pigment (alkannin), which was used as a paint and dye by Native Americans. The purple pigment sometimes stains herbarium sheets as well. The family is named after the Mediterranean genus Borago L., a name derived from the Latin word burra, meaning rough-hairy. Borago officinalis L. (borage) is among the few species in the family to be used as a culinary herb and is also grown for its ornamental and medicinal value.