Introduction to the Heliotropiaceae Family

The Heliotropiaceae family is another recent split out of the broader Boraginaceae family, so when you learn to identify the Heliotropiaceae, you will quickly see their many similarities.

The first time I encountered this family was hiking up to a lighthouse in Mazatlan, Sinaloa, Mexico, where I found a Tournefortia happily growing alongside the trail. I found its large scorpioid cymes rather beautiful, even though they are mostly white flowers. While mostly a tropical family, some species can be found as far north as Canada, and while you can find them in the United States, their highest concentration in North America appears to be in Mexico.

Common Botanical Description of the Heliotropiaceae Family

If you’re new to plant morphology, this guide is a perfect beginner’s description, with no need to know any scientific jargon. Below this section is additional information on uses and morphology photos to help you identify the family, followed by pictures of individual species found in North America. But for researchers or those wanting to learn a more in-depth version, refer to the Scientific Botanical Description below the images for highly detailed scientific descriptions and genus-level distribution data.

Leaves and Stems of the Heliotropiaceae: The Heliotropiaceae include many subshrubs or herbs, but also vines, shrubs, and even small trees, often with hairy stems and leaves. The leaves are simple and alternately arranged along the stem; they may or may not have leaf stalks (petioles), and the margins are usually smooth but may be toothed or folded backwards on the edges.

Flowers of the Heliotropiaceae: The flowers are usually found in characteristic coiled inflorescences called scorpioid cymes. Flowers are mostly bisexual, containing both male (stamens) and female (ovary, stigma, style) parts within the same flower. The sepals are fused at the base into a short tube with 5 spreading lobes. The corolla is also fused at the base with 5 lobes that are often white but can also be yellow, blue, pink, or orange.

Reproductive Features of the Heliotropiaceae: There are typically 5 stamens in the throat of the flower tube. The Heliotropiaceae family all possess a single style on top of their ovary with a unique cone-shaped stigma that is an easy way to identify the family when visible. However, since the reproductive features are usually hidden in the floral tube, it often requires dissection or a hand lens to see.

Fruits of the Heliotropiaceae: Fruits may be dry fruits or fleshy drupes (think cherry with a hard stony pit) but are usually 4-seeded and separate into 1–4 “nutlets.”

Uses of Heliotropiaceae 

Within the Heliotropiaceae, the Heliotropium genus is often used ornamentally, especially those with violet, purple, or fragrant flowers, like Heliotropium arborescens (garden heliotrope).

The Heliotropium genus is also the one most often used in traditional medicine to treat skin problems and wounds, with some being used to lower blood pressure, treat allergies, and act as a microbicide. Certain Euploca species have also been used to treat gastrointestinal, respiratory, and vascular disorders.

Morphology of Heliotropiaceae in North America

Some Heliotropiaceae Species Found in North America

Euploca convolvulacea—Phlox Heliotrope

This small annual grows up to 30 cm tall with small, fragrant white flowers that resemble the Convolvulaceae family, which is where its species name comes from. It is native mostly to the southwestern and south-central United States and south into northern Mexico. This one was in Oklahoma.

Euploca procumbens—Fourspike Heliotrope

This low-growing, hairy annual grows up to 50 cm tall but is more often procumbent. It has narrow scorpioid cymes of small white flowers. It is common and widespread throughout the tropical and subtropical Americas, especially common in Mexico and northwards into the central United States.

Heliotropium angiospermum—Scorpion’s Tail

This annual or short-lived perennial herb/sub-shrub has scorpioid inflorescences, typically rugose leaves, and can grow up to about 1 m tall. It is native throughout Mexico, Central America, the Antilles, northern South America, and in the USA in Texas and Florida.

Heliotropium indicum—Indian Heliotrope

This erect, branched annual with hairy stems and egg-shaped leaves can grow up to 50 cm tall and has small white or purple flowers. It is native to Asia but has been widely introduced to Africa, the southeastern USA, Mexico, the Antilles, Central America, and South America.

Heliotropium hartwegiana—Formerly Tournefortia hartwegiana

This wild plant is sometimes confused with the garden heliotrope. However, it is native to seasonally dry tropical or subtropical regions of Mexico and may also be found in extreme southern Arizona in the United States. It has congested scorpioid cymes with white or light flowers and rough-textured leaves.

Scientific Botanical Description of the Heliotropiaceae

Habit & Leaf Form of the Heliotropiaceae Family

The Heliotropiaceae family is a variable family in terms of form, including annual or perennial herbs, vines, subshrubs, shrubs, and small trees with a pubescent indumentum that is often strigose, sericeous, or rarely glandular.

The leaves are simple, alternately arranged, petiolate or sessile, with entire margins or rarely crenate or dentate, but often revolute or conduplicate. The lamina may be linear, elliptic, ovate to suborbicular, and the surfaces are often hispid to pubescent hairy and may be rugose or succulent.

Flowers of the Heliotropiaceae Family

The inflorescences are terminal or axillary thyrsoids, with most having distinct scorpioid cymose inflorescences, but sometimes they are absent. Flowers are bisexual (rarely unisexual), 5-merous, and possess a calyx that is mostly divided almost to the base, forming a short tube and a campanulate shape. The calyx is usually pubescent, and the aestivation is valvate.

The corolla is often white but can also appear in yellow, blue, pink, or orange. It is sympetalous with lobes that are linear to uborbicular. Aestivation is valvate (or nearly so), apert-duplicative, imbricate, or rarely quincuncial or cochlear.

Androecium of the Heliotropiaceae Family

The Heliotropiaceae have 5 stamens with filaments that are adnate to the corolla tube, with anthers usually included and not easily visible.

Gynoecium of the Heliotropiaceae Family

The gynoecium is bicarpellate, with a usually 4-locular ovary that is often deeply lobed, similar to the Boraginaceae. However, the style is terminal with a conical stigmatic head with a basal ring-shaped stigma and a sterile tip that is sometimes 2-lobed and a nectar disc present at the ovary base. The unique conical stigmatic heads are a synapomorphy for this family, which, when seen in a scorpioid inflorescence, are useful in making a positive identification

Fruit of the Heliotropiaceae Family

The fruit of the Heliotropiaceae may be fleshy drupes or dry schizocarps. Fruits are usually 4-seeded (rarely with 1–2 seeds), separating into 1–4 nutlets with 1–2 seeds each, but sometimes sterile chambers are also present.

Taxonomy of Heliotropiaceae

There are about 450 species in 4-6 genera in the Heliotropiaceae family in the Boraginales order of the core eudicots (dicots), depending on how the genera have been split or lumped. This family was historically treated as distinct from Boraginaceae until it was included as a subfamily, Heliotropioideae. It has also been included in the Ehretieae tribe within that now older definition of the Boraginaceae family. A 2016 revision, however, confirmed its status as a distinct family. For more information on the justification of this split, I strongly encourage you to check out Luebert et al. (2016) in the references below. For now, I am giving ranges of species and including Tournefortia which has mostly been placed in other genera, but until the sources can all agree, I am keeping it separate for now.

Genera of the Heliotropiaceae Family:

Euploca (66-172), Heliotropium (254-345), Ixorhea (1), Myriopus (15-25), and Tournefortia (67-106 most now included in Heliotropium, but some are in Myriopus).

Key Differences From Similar Families

The Heliotropiaceae were until recently a subfamily of the Boraginaceae, which is also known for its scorpioid cymes. However, the Boraginaceae is known for having more bristly and glandular hairs, and its usually deeply lobed ovary has a single gynobasic style rather than a terminal one with a cone-shaped stigma. Also, Boraginaceae mostly produce indehiscent nutlets instead of drupes with 4 stones or dry schizocarps.

The Hydrophyllaceae were another recent split from the Boraginaceae. They have scorpioid inflorescences but are mostly blue-to-violet in color, and they have a style with 2 stigmatic branches. They also produce dry capsules rather than drupes or schizocarps.

The Ehretiaceae are mostly shrubs and trees, with a terminal style with a bifid stigma, which could be confused with woody Heliotropiaceae. However, Ehretiaceae thyrsoidal inflorescences are not typically coiled like the Heliotropiaceae, and their fruits are mostly fleshy drupes.

The Cordiaceae is another recent split, but these are also mostly trees and shrubs with characteristic 4-lobed stigmas that make them easy to distinguish.

Distribution of Heliotropiaceae

The Heliotropiaceae have a worldwide distribution, nearly cosmopolitan with the noticeable exception of northern cool temperate climates, being mostly concentrated pantropically and in the subtropics. In the Americas, the family is found from southern Canada in the prairie provinces all the way south to the Patagonia region at the southern end of South America.

Distribution of Heliotropiaceae in the Americas

Canadian Genera Include:

Heliotropium 1 sp. is native to AB, SK, and MB.

USA Genera Include:

Euploca ~10 spp. are recognized on POWO and WFO as being present and native in most of the southern half of the states, but USDA-NRCS still says it is a synonym of Heliotropium; Heliotropium 23 spp., both native and intro to most of the USA, inc. HI, but excluding MN, MI, and WI; Tournefortia 2 spp. native in TX and FL, but these are sometimes classified under Myriopus.

Mexico Genera Include:

Euploca ~9 spp. native to all of Mexico, including 7 endemics; Heliotropium (including former Tournefortia) ~24 spp. native to all of Mexico; Myriopus 4? Mexico and neoendemic spp. native throughout Mexico. 

Neotropical Genera Include:

Euploca at least 30 spp., mostly endemics, found throughout CAM, the Antilles, and all of SAM except for Chile; Heliotropium 50-60 spp. (inc. former Tournefortia) native throughout the Antilles, CAM, and SAM; Ixorhea monospecific endemic of NW Argentina; Myriopus 25 mostly Mexican and neoendemic spp., is native from Mexico S through CAM, the Antilles, and tropical SAM to N Argentina, excluding N Chile.

Patagonia Genera Include:

Euploca 2? spp. are native to C+S Argentina; Heliotropium 1-2 spp. are native throughout the Patagonia region.

Additional Information and References

• Visit Lyrae’s Dictionary of Botanical Terms to learn the terminology of botanists. Note that if you hover over most of the words in the articles, you can also get their definitions there.
• Willis, Lyrae (Unpublished). Plant Families of North America. This source is where all of the family descriptions come from. Below should be most of my references for this project, along with my own personal observations throughout North America.
• Alawfi, M. S., Alzahrani, D. A., & Albokhari, E. J. (2024). Complete Plastome Genomes of Three Medicinal Heliotropiaceae Species: Comparative Analyses and Phylogenetic Relationships. BMC plant biology, 24(1), 654. https://doi.org/10.1186/s12870-024-05388-8.
• Canadensys: Acadia University, Université de Montréal Biodiversity Centre, University of Toronto Mississauga, University of British Columbia. http://data.canadensys.net/explorer (accessed 2020 – current).
• FNA (1993+). Flora of North America. https://floranorthamerica.org/Main_Page. Accessed 2022-current.
• GBIF.org (2020+), GBIF Home Page. Available from: https://www.gbif.org
• iNaturalist.org (2020+). https://www.inaturalist.org/. Accessed 2020-current.
• Luebert, F., Cecchi, L., Frohlich, M. W., Gottschling, M., Guilliams, C. M., Hasenstab-Lehman, K. E., Hilger, H. H., Miller, J. S., Mittelbach, M., Nazaire, M., Nepi, M., Nocentini, D., Ober, D., Olmstead, R. G., Selvi, F., Simpson, M. G., Sutorý, K., Valdés, B., Walden, G. K., & Weigend, M. (2016). Familial Classification of the Boraginales. axon, 65(3), 502–522. https://plants.sdsu.edu/amsinckiinae/pdfs/Luebert_etal2016-Boraginales.pdf.
• Naturalista: CONABIO http://www.naturalista.mx (Accessed 2020–current).
• Neotropikey: Milliken, W., Klitgård, B., & Baracat, A. eds. (2009+). Neotropikey: Interactive key and information resources for flowering plants of the Neotropics. www.kew.org/neotropikey.com (accessed 2020 – current).
• Patagonia Wildflowers: Wildflower Identification Site. https://patagoniawildflowers.org/ Accessed throughout the fall of 2020.
• POWO (2019+). Plants of the World Online. Facilitated by the Royal Botanic Gardens, Kew. Published on the Internet: http://www.plantsoftheworldonline.org/
• Stevens, P. F. (2001+). Angiosperm Phylogeny Website. Version 14, July 2017 [more or less continuously updated since]. http://www.mobot.org/MOBOT/research/APweb/
• USDA, NRCS. 2020. The PLANTS Database (http://plants.usda.gov, 2 June 2020). National Plant Data Team, Greensboro, NC, USA; Accessed 2020-present.
• Watson, L., and Dallwitz, M.J. (1992+). The Families of Flowering Plants: descriptions, illustrations, identification, and information retrieval. Version: 2nd May 2020. delta-intkey.com. Accessed spring through fall of 2020.
• WFO (2022): World Flora Online. Published on the Internet: http://www.worldfloraonline.org. Accessed Spring 2022 – current

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I am currently seeking funding to expand my website and SEO capabilities as I keep adding new families, and I am also looking to invest in a new macro lens, as I will soon be adding floral dissections to the families as they become available to me. You can donate to help support native plant education using the GoFundMe link, also at the bottom of the page.

Copyright Information

The information and the photos on this site are free to use for educational purposes, with proper attribution. For other uses, please contact me first.

You can cite this site as follows: Willis, Lyrae (2020+). Lyrae’s Nature Blog – Plant Families of North America. https://lyraenatureblog.com/. Accessed [Enter Date].