Introduction to the Cleomaceae Family

Welcome to the Cleomaceae, or spiderflower, family of plants, a group of interesting, often sticky and smelly plants with pretty flowers that are closely related to the mustard, or Brassicaceae, family. This family has undergone a lot of work, and my description here recognizes the work of Roalson and others who have been working to resolve issues with the far too large Cleome genus and better recognize the distinctiveness of the genera native to the American continents, among other issues. But, as soon as new information comes available, I will update it!  

If you’re new to plant morphology, the guide below is a perfect beginner’s description if you want to learn how to identify the spiderflower or Cleomaceae family, with no need to know any scientific jargon.

Below the guide, you’ll find morphology photos to help you identify the features of the Cleomaceae family, information on uses and wildlife values, and pictures of individual Cleomaceae species I have photographed in North America, organized by supertribe and tribe, so you can start to see the relationships within the family as well.

Beginner’s Guide to the Spiderflower (Cleomaceae) Family

For researchers or those wanting to learn more, further down the page is a Scientific Botanical Description and my genus-level distribution data throughout North, Central, and South America.

Leaves and Stems of the Spiderflower Family

The Cleomaceae, or spiderflower family, are mostly annual herbs, but they can be perennial herbs, shrubs, trees, and vines. Plants are often resinous or have sticky hairs that are often pungent-smelling.

Leaves are alternately arranged along the stem, arranged on leaf stalks (petioles), and are usually compound, made of usually 3-7 leaflets each. The leaves are often hairy, and the margins are either smooth or finely toothed.

Flowers of the Spiderflower Family

The spiderflower family has mostly bisexual flowers with both male (stamens) and female (ovary, style, and stigma) parts in the same flower, typically in clusters at the stem tops but sometimes solitary in leaf axils.

Flowers have 4 sepals and 4 petals and a long, prominant stalk (gynophore) that the ovary sits on, usually with nectaries at their base. Petals are arranged cross-like (cruciform) or fan-like (strongly zygomorphic) and come in white, pink, purple, bright yellow, red, or orange.

Reproductive Features of the Spiderflower Family

Spiderflowers typically have 6 stamens but may have 4-100, rarely more, some of which may be infertile and petal-like, and they typically sit at the base of the stalk the ovary sits on (gynophore). Stamens are usually very long and extend far past the petals, giving them a spidery look and their common name, but they are shorter in some genera.

The ovary sits on a long stalk (gynophore) above the petals and sepal attachment, and it has a variable style ranging from none (the stigma sits directly on the ovary) to a very long style that persists in fruit.

Fruits of the Spiderflower Family

Spiderflowers almost always produce pod-like fruits that look like legumes (but are called siliques or silicles), are often on long stalks (gynophores), and contain 1-100+ rounded, kidney-shaped, or horseshoe-shaped seeds.

Morphology of Cleomaceae in North America

Some Species of Cleomaceae Found in North America

Arivela (Cleome) viscosa—Asian Spiderflower

Arivela viscosa is an Old World species of Cleomaceae that has also been introduced to the southern USA and south throughout the neotropics; this one was found in western Mexico. It is still usually called by its former name under the much broader category of Cleome s.l. It is an annual herb up to 1.5 m tall covered in pungent, sticky glandular hairs. It has compound leaves with 3-5 leaflets and bright yellow flowers with a variable number of stamens, usually 12-30, unlike those of Cleome s.s. (the more restricted definition), which has only 6. Fruits are glandular-hairy and erect or ascending pod-like fruits (siliques).

Cleomella lutea—Yellow Bee Plant

This pretty Cleomaceae member is Cleomella lutea here showing off its bright yellow 4-petaled flowers with 6 prominent stamens that extend far past the petals, giving them a spider-like appearance, and pod-like fruits up to 3.5 cm long (siliques) on long stalks (gynophores). It is an annual herbaceous plant that grows up to 1 m tall, with smooth, hairless stems and hairless compound leaves made of 3 or sometimes 5 leaflets. It is native to the western United States and northwestern Mexico, where it serves as a critical mid-to-late-summer nectar source in arid habitats. This one was near Woodside, Utah, USA.

Cleomella serrulata—Rocky Mountain Bee Plant

Cleomella serrulata is another transfer, formerly part of Peritoma, but that genus was transferred by Roalson & J.C. Hall to Cleomella. It is an annual herb, 30–150 cm tall, with a pungent odor when bruised. Compound leaves, mostly hairless, have 3 leaflets. Flowers are a pretty purplish or pinkish, rarely white, and they have 6 long, protruding stamens. Podlike fruits droop on long stalks (gynophores) when mature. This plant is native to western and central Canada and the United States, extending south into northern Mexico. This one was near Laverne, Oklahoma, USA.

Uses of the Cleomaceae Family

The Cleomaceae have frequently been used by indigenous groups around the world as leafy vegetables, similar to mustard greens. Cleome serrulata was also widely used in traditional pottery in the American Southwest.

Some of the Cleome species are also used ornamentally for their striking flowers, long stamens, and adaptability to hot, drought-prone climates. They are also used for honey production due to their high sugar content and accessible floral parts that allow for easy collecting by the honey bees.

Ecosystem and Wildlife Values of the Cleomaceae

One of the biggest ecological values the Cleomaceae bring is their abundant nectar that supports countless native bees, solitary wasps, hoverflies, butterflies, and even some hummingbirds.

Just like others of the Brassicales, their glucosinolate (the mustard oils) content resists general herbivores but makes them an essential host plant for pierid butterflies, especially the whites.

Since many are fast-growing annuals with high drought and stress tolerance, they act as an early pioneer species in disturbed habitats where they help stabilize the soil.

Finally, the seeds are an important food source for songbirds, game birds, and small rodents.

Taxonomy of the Cleomaceae Family

The Cleomaceae family has approximately 270 species in 15-27 genera of the Brassicales order within the core Eudicots. The Cleomaceae were all once formerly included as a tribe or subtribe of the Capparaceae family until modern phylogenetics showed that they were more closely related to the Brassicaceae, and they were given their own family status.

However, there has also been significant generic revision from a broadly circumscribed, massive Cleome genus with over 200 species, including different sections or subgenera that were split into numerous distinct, monophyletic genera instead. Depending on whether authors accept a broader and more conservative view or a more modern phylogenetic view, there are currently about 15-27 genera instead of the original 3 I had when I first worked with this family.

And, as with most things in plant taxonomy these days, work is still being done, so the generic descriptions of this family may yet change again. I will update this page as soon as new information is available.

Genera of the Cleomaceae Family:

My current delineation of the Cleomaceae family is based on modern treatments (e.g., Roalson et al. 2015; Barrett et al. 2017; Roalson & Hall 2017; Bayat et al. 2018; McGinty & Roalson 2020; Roalson 2021; Soares Neto & Roalson 2022), so databases like Plants of the World using legacy delineations are not yet in sync with this.

Andinocleome (6-8), Areocleome (1), Arivela (10-12), Cleome s.s. (22), Cleomella (22-25), Coalisina (6), Corynandra (17-20), Dactylaena (7), Dipterygium (1), Gilgella (1), Gynandropsis (1-2), Haptocarpum (1), Iltisiella (2), Kersia (8-10), Melidiscus (1), Physostemon (10 inc. Mitostylis), Podandrogyne (25-50* *more Andean species awaiting formal publication), Polanisia (5), Pterocleome (1), Rorida (20-25), Sierulea (30-45?), Stylidocleome (2), Tarenaya (38), Thulinella (1).

Key Differences From Similar Families

Mostly the Cleomaceae are confused with others in the Brassicales order. The Capparaceae also share 4-merous flowers, long stamens, and a long gynophore, but they are almost exclusively woody trees or shrubs that mostly lack glandular hairs instead of herbs with sticky, often foul-smelling glandular hairs.

The Brassicaceae are mostly herbs with 4 cruciform petlas, 6 stamens, and 2-valved siliques, but they can usually be identified by the lack of a gynophore (the ovary is sessile) and their tetradynamous stamens rather than mostly equal stamens that are usually exserted and may be polystemonous.

Sometimes when in fruit they can be confused with the Fabaceae family because of their pod-like fruits and palmately compound leaves. However, most Fabaceae produce unique pea-like (papilionaceous) flowers or actinomorphic brush-like flowers instead of flowers with 4 clawed petals and long-exserted stamens.

Finally, they are also occasionally confused with the Onagraceae because they also have 4 prominent petals, showy stamens, and pod-like capsules, but Onagraceae also have inferior ovaries (attached below the calyx), and their leaves are simple instead of typically palmately compound.

Scientific Botanical Description of the Cleomaceae Family

This is the more in-depth scientific description of the Cleomaceae family with more granular detail than was provided in the guide above for those who want more information.

Habit & Leaf Form of the Cleomaceae Family

The Cleomaceae are mostly annual herbs, but they also include some perennial herbs and a few shrubs, trees, and lianas. Plants are often characteristically resinous or with glandular-pubescent hairs that are often sticky and may be aromatic, foetid, or odorless (by contrast with Capparidaceae), although some woody Andean taxa or other dry-adapted species can be glabrescent.

Leaves are arranged in an alternate spiral and are petiolate and non-sheathing. The lamina is usually palmately compound with 3-7(-9) leaflets, or sometimes unifoliate or simple. Leaf margins are entire to serrulate.

Stipules may be minute to scaly, leafy, hair-like, modified into stipular spines, or absent.

Leaf lamina is dorsiventral to isobilateral/centric. Abaxial epidermis may be papillose or have epicuticular wax, or neither. Stomata are present and predominantly anomocytic. Leaves usually have hairs, which are mostly multicellular capitate-glandular hairs.

Flowers of the Cleomaceae Family

The Cleomaceae are mostly hermaphroditic, sometimes andromonoecious, or rarely functionally unisexual or dioecious (e.g., Podandrogyne). Flowers are arranged in terminal or axillary bracteate racemes or may be solitary in upper leaf axils.

Flowers are actinomorphic to strongly zygomorphic. The floral receptacle expands into a prominent gynophore, androphore, or a combined androgynophore, elevating the reproductive organs above the perianth. Nectaries are present in the form of a hypogynous disk or distinct adaxial glands or scales.

The perianth has a distinct calyx and corolla with typically 8 parts (4–12) in 2 whorls. The calyx typically has 4 sepals in 1 whorl or more or less resolvable into decussate K2+2, which are free or basally connate, equal to unequal, persistent or caducous, with aestivation that is imbricate, valvate, or open in bud.

The corolla has 4 petals (2–6) in 1 whorl that are free and often strongly clawed at the base with linear or orbicular limbs. They may appear cruciform or be strongly zygomorphic when arranged in a fan-like array. Petals vary in color, including white, pink, purple, bright yellow, red, or orange.

Androecium of the Cleomaceae Family

The androecium of the Cleomaceae are made of 4 to 100 members or rarely 250+ when primordia undergo secondary branching with anthers maturing centrifugally (e.g., Corynandra and Kersia) or are reduced to 1-2 (Dactylaena), but most members have 6 stamens that are rarely tetradynamous (c.f. Brassicaceae).

Members are free from the perianth, inserted on the receptacle, at the base of the gynophore, or borne along an androgynophore. Filaments may be equal or not and are usually strongly exserted but are sometimes slender and thread-like, but they only rarely have swollen or winged appendages.

The androecium may consist entirely of fertile stamens, or it may feature infertile, petalloid, or reduced staminodes.

Anthers are basifixed to dorsifixed, tetrasporangiate, and dehiscing via longitudinal parallel slits.

Gynoecium of the Cleomaceae Family

The Cleomaceae have a syncarpous gynoecium that is superior and consists of 2 fused carpels forming a 1-locular ovary; while a persistent replum is present, there is no complete septum (c.f. Brassicaceae) dividing the cavity.

The gynoecium ranges from non-stylate with a sessile stigma to highly elongated and persistent in fruit. Stigmas are capitate, truncate, or 2-lobed, dry or wet type, and are usually papillate.

Placentation is parietal along 2 (rarely 3) placental lines, with 2 to 100+ ovules per locule. Seeds are campylotropous or amphitropous, bitegmic, and crassinucellate.

Fruit of the Cleomaceae Family

The Cleomaceae overwhelmingly produce dry, 2-valved, unilocular, elongated siliques or silicles. Dehiscence is valvular, with the two valves separating from the persistent replum. Less often, fruits may be indehiscent and schizocarpic, breaking into 1-seeded, nut-like mericarps. Fruits are sessile or often elevated on a gynophore/androgynophore.

Fruits typically contain 1-100+ seeds, which are somewhat rounded, reniform, or horseshoe-shaped, and in many clades, the seeds feature a prominent invaginated cleft or an elaiosome/aril. Endosperm is sparse or absent.

Distribution of the Cleomaceae Family

The Cleomaceae family has a widespread subcosmopolitan distribution from the north and south temperate (mostly warm temperate) to tropical zones, although it is noticeably absent from much of the cold temperate regions of the Northern Hemisphere. In the American continents, they are found from southern Canada south to Argentina but do not reach the colder Patagonian region of South America.

Distribution of the Cleomaceae in the Americas

Canadian Cleomaceae Genera:

Cleomella (Peritoma) 1 sp. native to BC, AB, SK, and MB and intro to ON and QC; Polanisia 1 sp. NAM endemic genus native to AB, SK, MB, ON, and QC; Tarenaya 1 sp. intro to ON, QC.   

USA Cleomaceae Genera:

Cleome 1 sp. introduced to the southern USA; Cleomella ~20 spp. native to most of the USA except SC, NC, and ME and introduced to WI, IL, IN, OH, and CT, about half are endemic to the USA; Polanisia 5 spp. NAM endemic genus native throughout the USA, especially in the Great Plains, but is absent in ME, NC, and SC, includes three south & central USA endemics; Sierulea 1 sp. intro to the southern USA; Tarenaya 3 spp. inc. 1 native to the extreme southern states and 2 spp. widely introduced.

Mexico Cleomaceae Genera:

Cleome 2 spp. intro throughout Mexico; Cleomella 9 spp. native throughout Mexico, including 3 endemics; Cleoserrata 2 spp. native to southern Mexico; Dactylaena 1-2 spp. mostly neoendemic genus native to southern Mexico; Iltisiella 2 spp. mostly Mexico endemic genus native throughout Mexico, especially the western and northern dry regions; Physostemon 1 sp. neoendemic genus native to southern Mexico; Polanisia 1 sp. NAM endemic genus native to most of Mexico; Tarenaya 2 spp. native across most of Mexico.  

Neotropical Cleomaceae Genera:

Andinocleome 6-8 spp. SAM (the Andes) endemic genus of Venezuela, Colombia, Ecuador, Peru, Bolivia, and Chile; Cleome 3 spp. Old World genus intro to the Caribbean Islands, Bermuda, the Bahamas, Galapagos, Central America, and tropical South America; Cleoserrata ~5 spp. Mexico and neoendemics native to CAM, the Antilles, and SAM exc. Uruguay and Chile; Dactylaena 7 spp. neoendemic genus of Haiti, Venezuelan Antilles, Venezuela, E Brazil, Bolivia, and NW Argentina; Haptocarpum monospecific narrow endemic of E Brazil in the Bahia region; Iltisiella 2 spp. mostly Mexico endemic genus native in northern CAM; Melidiscus monospecific neoendemic native to Panama, scattered throughout the Caribbean, and native to SAM S to Bolivia and Brazil; Physostemon 10 spp. neoendemic genus native to CAM, the Greater Antilles, Brazil, Venezuela, Guiana, Paraguay, and Argentina; Podandrogyne has roughly 25-50 spp. (many Andean species awaiting formal publication.) neoendemic genus from Costa Rica S through Colombia and Ecuador with the most species, also in Peru, Bolivia, and Amazonian Brazil; Pterocleome monospecific narrow N SAM endemic centered in Colombia and Brazil; Sierulea 1 sp. intro to the Caribbean, CAM, and N SAM; Tarenaya ~35 spp. mostly neoendemic genus (1 disjunct sp. in Africa) native to CAM, the Caribbean, and tropical SAM S to Argentina (exc. Chile), with a center of diversity concentrated in E+C Brazil.

Patagonia Cleomaceae Genera:

Absent

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 definitions from them there.
• Willis, Lyrae (Unpublished). Plant Families of North America. This is where all of the family descriptions come from. Below should be most of my references for this, along with my own personal observations throughout North America.
• Bayat, S., Schranz, M. E., Roalson, E. H., & Hall, J. C. (2018). Lessons from Cleomaceae, the sister of crucifers. Trends in Plant Science, 23(9), 808–821. https://www.cell.com/trends/plant-science/abstract/S1360-1385(18)30140-7
• 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. If you like plants or nature in general, please join the iNaturalist community and start sharing your observations with others. The data we track is invaluable for scientists like me wanting to track population changes over time.
• McGinty, E. M., & Roalson, E. H. (2020). Pterocleome (Cleomaceae), a new genus for an Andean clade. Phytotaxa, 456(3), 266–274. https://www.biotaxa.org/Phytotaxa/article/view/phytotaxa.456.3.3
• Naturalista: CONABIO http://www.naturalista.mx (Accessed 2020–2022).
• 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/. Accessed 2020-current.
• Roalson, E. H. (2021). A circumscription of Cleome s.s. (Cleomaceae). Phytotaxa, 496(1), 54–68. https://phytotaxa.mapress.com/pt/article/view/phytotaxa.496.1.2
• Roalson, E. H., Hall, J. C., Riser, J. P., II, & Cochrane, T. S. (2015). A recircumscription of Cleomella (Cleomaceae) to include Peritoma, Wislizenia, and Oxystylis. Taxon, 64(4), 708–730. https://www.researchgate.net/publication/279852219_A_revision_of_generic_boundaries_and_nomenclature_in_the_North_American_cleomoid_clade_Cleomaceae.
• Soares Neto, R. L., Thomas, W. W., Roalson, E. H., & Barbosa, M. R. V. (2022). Taxonomic revision of Tarenaya (Cleomaceae). Annals of the Missouri Botanical Garden, 107, 250–313. https://doi.org/10.3417/2022705
• 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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You can cite this site as Willis, Lyrae (2020+). Lyrae’s Nature Blog – Plant Families of North America. https://lyraenatureblog.com/