Introduction to the Iridaceae Family

Welcome to the Iridaceae, aka the Iris family! This popular family is native across the globe, from sun-drenched South African hillsides to soggy North American wetlands. This family is easy to recognize by their sword-shaped leaves that often overlap in a fan-shaped arrangement and their unique colorful three-part flowers (6 tepals, 3 styles, 3 stamens) that usually have showy, often yellow nectar guides.

I am a big ‘fan’ of this family (sorry, botany nerd alert!) because it’s so beautiful and so diverse, and I never understood why people grow invasive irises in their gardens when we have so many gorgeous native ones to choose from! (But never harvest from the wild, please!). And since I remember my mom also being a fan of irises, I am dedicating this page to her memory.

Common Botanical Description

If you’re new to plant morphology, this guide is a perfect beginner’s description for learning to identify the Iridaceae family, with no need to know any scientific jargon. Below this section are 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 Iridaceae: The Iridaceae are mostly perennial herbs from rhizomes or corms, often growing near or partially submerged in water, but drought-tolerant species are also known. Leaves are simple, grass-like or swordlike, with parallel veins, and often borne edgewise to the stem and appearing fan-shaped.

Flowers of the Iridaceae: The plants are hermaphrodites, with male (stamens) and female (ovary, stigma, style) parts in the same flowers. Flowers are small to large, made of six petal-like tepals that are joined and appear in two whorls, with the inner whorl often smaller and sometimes standing upright, a distinguishing feature in the family. The flower/inflorescence has a leafy sheath around it that they emerge from as they bloom.

Reproductive Features of the Iridaceae: There are usually 3 stamens, free or joined in a tube, appearing in one whorl opposite the outer tepals. They almost always have an inferior ovary attached beneath the point where the tepals attach, and they may have 1, 3, or 6 terminal styles, depending on whether these are interpreted as lobes or separate styles, but they usually ‘appear’ to have 3.

Fruits of the Iridaceae: Fruits are dry capsules that split open at maturity and usually contain 3 chambers with 2 rows of large seeds in each.

Uses of Iridaceae 

The Iridaceae are widely grown as ornamental plants, including the common blue flag, the yellow flag, and the lovely Dietes species, all of which can become invasive in some areas. Many species of Iridaceae are, however, narrow endemics, with small populations and/or few occurrences, making them highly vulnerable to extirpation and extinction. This is one of the many reasons we should never remove plants from the wild.

Crocus sativus is the most prized member of the family, a delicate flower grown for the world’s most expensive spice, saffron, which comes from the 3 thread-like stigmas of the flowers. Harvesting 3 tiny red stigmas from each flower means it takes 75,000 to 150,000 flowers just to get a pound of dried saffron.

Ecosystem and Wildlife Values of Iridaceae

The Iridaceae are popular with pollinators like bees, moths, and butterflies for their nectar and pollen, including highly visual flowers with unique ultraviolet patterns and nectar guides to invite the insects in. Many gladiolas have even evolved for specific moth species, where the shape of the flower matches that species’ tongue length.

In North America, native irises often live as emergent aquatics or wetland species with their dense rhizomes that stabilize the shoreline and create microhabitats for invertebrates.

Morphology of Iridaceae in North America

Some Species of Iridaceae Found in North America

Iridoideae Subfamily

Dietes grandiflora—Fortnight Lily

This plant is a popular cultivated species in North America for its hardiness and large, beautiful flowers. From South Africa, this species has 6 white tepals, 3 petal-like white styles in the center, and 3 yellow nectar guides on the outer tepals to guide the pollinators in. This one was in cultivation in Mazatlan, Sinaloa, Mexico.

Iris cristata—Dwarf Crested Iris

This lovely iris is native to the quiet forests of the southeastern USA, like this one I found in Georgia. It has low, sword-like leaves growing in a fan-like arrangement. The flower has 6 purple tepals, with nectar guides on the outer 3 and 3 thinner inner ones that stand slightly upright. However, don’t be fooled by the innermost whorl of the slightly lighter purple upright ‘tepals’—those are actually petal-like styles!

Iris fulva—Copper Iris

This moisture-loving iris stands out for its bright coppery-red to brick-red flowers, unusual in the family, and for its 3 inner tepals that droop like the outer ones instead of standing upright. Those 3 upright ones in the middle are petal-like styles, and you can see the open stylar canal at the end of the one in the front. These were growing in a wet roadside ditch in Arkansas.

Iris missouriensis—Rocky Mountain Iris

This Iris thrives in high-elevation meadows, plains, and mountain valleys from Canada to Mexico; this one was in the Sacramento Mountains of New Mexico. The flowers are pale to dark lavender with striking purple veins, but I have also found it in the rare white form with yellow veins. The inner tepals stand upright along with the petal-like styles.

Sisyrinchium angustifolium—Blue-Eyed Grass

This genus is known for its grass-like leaves and small, usually blue-violet flower that only open on bright, sunny mornings. Sheaths are visible at the flower base, and if you look at the back of the flower, a fuzzy green inferior ovary is clearly visible. This species is native to low woods, meadows, and damp fields in eastern North America, like this one I found in Tennessee.

Sisyrinchium micranthum—Striped Rush-Leaf

This is an introduced, weedy species from South America. It can be identified by its small flowers, which may be light lavender, blue, or creamy white. They can be identified by the prominent wine-colored band at the tepal base, which makes a contrasting ring around its central yellow throat and its wine-colored veins on the tepals. This one was on a moist roadside in Mississippi.

Sisyrinchium pruinosum—Spotted Blue-Eyed Grass

This lovely native species is a bit unusual in that it thrives in sun-baked prairies and grasslands, like this one I found in Oklahoma. It has vibrant blue flowers that are larger than most of its genus, and its leaves are pruinose—with a waxy, grayish, powdery coating on the leaves that gives it its ‘spotted’ or ‘dotted’ appearance and common names. Its 3 stamens are also visible here, which are united into a tube at their base with 3 free yellow anthers at the top.

Scientific Botanical Description of the Iridaceae Family

Habit & Leaf Form of the Iridaceae Family

The Iridaceae are mostly perennial herbs, rarely shrubs, with or without a basal aggregation of leaves. They are mostly rhizomatous or cormous but sometimes are bulbaceous. Often helophytic, but sometimes xerophytic.

Leaves are persistent or deciduous, alternate, usually distichous, flat or terete, herbaceous or leathery, sessile or petiolate, and odorless or sometimes foetid. Leaves are sheathing, with free or joined margins. Blades are simple, borne edgewise to the stem (often in two rows appearing fan-shaped) or with blades normally orientated. The lamina is entire and linear or lanceolate, with parallel veins and no cross-venules, and is dorsiventral, bifacial, or centric. Stomata are anomocytic. Lamina has secretory cavities filled with mucilage, while the mesophyll lacks mucilage cells but contains crystals.

Flowers of the Iridaceae Family

Iridaceae are hermaphrodites that usually have floral nectaries with secretion from the nectaries at the tepal bases (mostly) or from the gynoecium via septal nectaries in Ixioideae. Pollination is mostly entomophilous, sometimes ornithophilous, or rarely anemophilous. Flowers are solitary or aggregated in panicles, cymes, spikes, umbels, or corymbs, with ultimate inflorescence units when more than one flower is cymose or racemose. Inflorescences are spatheate (via one or two expanded bladeless sheaths) and nearly always scapiflorous, but some are reduced to a single almost sessile flower (Crocus) and are often difficult to interpret.

Flowers are small to large, actinomorphic or zygomorphic, 3-merous, tetracyclic (usually), and bracteate. A perigone tube is present, long or short. The perianth is made of 6 joined tepals in 2 whorls, which may be similar or different in the two whorls (the inner whorl is sometimes much smaller). It is isomerous and petaloid, appearing in white, yellow, red, purple, violet, blue, or blue-green. The three outer petals often spread horizontally, while the three inner petals stand upright, and the flower is often spotted.

Androecium of the Iridaceae Family

There are 3(2) androecial members, made up of exclusively fertile stamens that are free of the perianth or adnate to the tube and either free of others or coherent with filaments, often united into a basal tube (1 adelphous). Stamens appear in 1 whorl, alternating with the outer perianth lobes. Anthers are separate from one another (usually) or cohering (sometimes Homeria); basifixed; dehiscing via longitudinal slits; extrorse.

Gynoecium of the Iridaceae Family

The gynoecium is 3-carpeled and often partly petaloid, but it may be non-petaloid. The pistil is nearly always 3-celled, or only 1 cell in Isophysis. The gynoecium is synstylovarious and nearly always inferior and 3-locular, with the odd carpel anterior, or very rarely superior and 1 locular in Isophysis.

Styles 1, 3, or 6, depending on the interpretation of the lobes, which may be deeply subdivided and slender (Nemastylis), but they are also very often widely expanded and petaloid. Generally, the styles are interpreted as 3 or 1 trilobed styles. Styles are terminal, and a stylar canal is present. Stigmas are dry type, papillate, and Group II type. Placentation is nearly always axile except when unilocular, then parietal. Ovules are 2–50(1) per locule; arillate or non-arillate; anatropous; bitegmic; crassinucellate.

Fruit of the Iridaceae Family

The fruits are always(?) non-fleshy, dehiscent loculicidal capsules. Capsules usually form behind flowers on the stalk side with 2 rows of large seeds in each locule. Seeds are endospermic and oily, but usually without starch.

Taxonomy of the Iridaceae Family

There are between 2,145 and 2,244 species in 66 genera in the Iridaceae family, which is part of the Asparagales order of the Monocot clade. As it is a relatively large family, broken into 7 subfamilies as follows:

1. Aristeoideae is a monogeneric subfamily that can be easily recognized because they are rhizomatous vines from southern Africa and Madagascar with isobifacial leaves and flowers that do not last long.
2. Crocoideae is a large subfamily with 1,170 species in 32 genera, mostly in southern Africa, but also in Europe, Arabia, and Central Asia. They are plants that grow from corms with spicate inflorescences with long-lived flowers and leaves with closed leaf sheaths.
3. Geosiridoideae is a small monogeneric subfamily with 1 genus and 3 species found in Madagascar, the Comores, and Australia. They are achlorophyllous mycoheterotrophic plants without styloids, with heterobifacial leaves, and with sessile flowers.
4. Iridoideae is a large subfamily with 920 species in 30 genera found worldwide, but especially in the spine of Central America and South America. They are plants whose whorls of tepals are always differentiated, and they have long, tubular style branches. They come from corms or sometimes bulbs, and the leaf blades may be rounded to flat or dorsiventral. Sometimes the tepals are bearded, and sometimes the style branches are commissural.
5. Isophysidoideae is a monospecific subfamily, Isophysis tasmanica, from Tasmania. It produces solitary flowers with spathes, and it has no nectaries, a more or less superior ovary, and style branches that are more or less spiraling and are commissural.
6. Nivenioideae is a small subfamily with 15 species in 3 genera found only in the southwest Cape region of South Africa. They are woody plants with long-loved sessile flowers and leaves with non-vascular fibrous strands and simple stigmas that are slightly expanded or not expanded at all.
7. Patersonioideae is a monogeneric subfamily with 34 species in Malesia, New Caledonia, and the shores of Australia. They are more or less woody, whizomatous plants with inner tepals that are absent or reduced to scales and broad stigma lobes.

Genera of the Iridaceae Family:

Aristeoideae: Aristea (60).

Crocoideae: Afrocrocus (1), Afrosolen (15), Babiana (93), Chasmanthe (3), Codonorhiza (7), Crocosmia (8), Crocus (257), Cyanixia (1), Devia (1), Dierama (43), Duthiastrum (1), Freesia (16), Geissorhiza (106), Gladiolus (296), Hesperantha (90), Ixia (101), Lapeirousia (28), Melasphaerula (1), Micranthus (7), Pillansia (1), Radinosiphon (2), Romulea (114), Savannosiphon (1), Sparaxis (16), Syringodea (6), Thereianthus (11), Tritonia (30), Tritoniopsis (23), Watsonia (53), Xenoscapa (3), Zygotritonia (7).

Geosiridoideae: Geosiris (3).

Iridoideae: Alophia (6), Bobartia (17), Calydorea (21), Cipura (10), Cobana (1), Cypella (35), Dietes (6), Diplarrena (2), Eleutherine (3), Ennealophus (6), Ferraria (18), Gelasine (8), Herbertia (12), Hesperoxiphion (5), Iris (320), Larentia (3), Libertia (17), Mastigostyla (29), Moraea (235), Nemastylis (4-6), Neomarica (1?), Olsynium (18), Orthrosanthus (9), Salpingostylis (1), Sisyrinchium (212), Solenomelus (2), Tapeinia (1), Tigridia (63), Trimezia (77).

Isophysidoideae: Isophysis (1).

Nivenioideae: Klattia (3), Nivenia (11), Witsenia (1).

Patersonioideae: Patersonia (26).

Key Differences From Similar Families

The Iridaceae can sometimes be confused with other bulbous plants of the Liliaceae. However, Liliaceae have 6 stamens and a superior ovary instead of 3 stamens and an inferior ovary in the Iridaceae.

They may also be confused with bulbous Amaryllidaceae. However, while Amaryllidaceae have inferior ovaries (and some superior) they usually have 6 stamens and only very rarely have 3. 

Distribution of the Iridaceae

The Iridaceae family consists of widespread, almost cosmopolitan species that are noticeably absent only from the frigid areas of northern Eurasia. In the Americas it is found from Arctic Canada and Greenland south through the USA, Mexico, Central America, and all of South America down to Tierra del Fuego.

Distribution of the Iridaceae in the Americas

Canadian Genera Include:

Crocoideae: Crocosmia 1 sp. intro BC; Crocus 1 sp. intro ON. Iridoideae: Iris 17 spp. are native in all of Canada, including the Arctic, but excluding NT and intro BC; Olsynium 1 sp. native to BC; Sisyrinchium 12 spp. are native throughout all of Canada, including the Arctic (and 1 sp. Greenland), but excluding NU. 

USA Genera Include:

Aristeoideae: Aristea 1 sp. intro HI. Crocoideae: Chasmanthe 1 sp. intro CA; Crocosmia 1 sp. intro OR, CA, TX, MS, FL, GA, SC, NC, and HI; Crocus 6 spp. intro OR, UT, VA, DE, NY, CT, MA; Freesia 2 spp. introduced in CA, FL; Gladiolus 7 spp. intro CA, AR, LA, MS, AL, GA, FL, SC, NC, VA, TN, KY, IL, OH, PA; Ixia 3 spp. intro CA; Romulea 1 sp. intro CA; Sparaxis 2 spp. intro CA; Watsonia 3 spp. intro to CA and HI. Iridoideae: Alophia 1 sp. native to TX, OK, AR, LA, MS; Calydorea 1 sp. native to FL, GA; Herbertia 1 sp. introduced to TX, LA, MS, FL; Iris 45 spp. native and intro in all of the USA and native to AK; Libertia 1 SAM sp. intro CA; Moraea 2 spp. intro CA; Nemastylis 4 spp. native AZ, TX, OK, KS, MO, AR, LA, MS, TN, FL, inc. 3 endemics, which inc. 1 narrow endemic of FL; Olsynium 1 sp. native to WA, OR, CA, NV, UT, ID; Salpingostylis monospecific endemic of FL; Sisyrinchium 39 spp. native and intro in all of the USA, inc. HI; native to AK; Trimezia 1 sp. intro FL and HI.

Mexico Genera Include:

Crocoideae: Crocosmia 4 spp. intro NL S throughout S Mexico; Freesia 1 sp. intro Tlx, Chp; Gladiolus 3 spp. intro Jal, Gto S to Chp; Melasphaerula 1 sp. intro Ver. Iridoideae: Alophia 4 spp. native to Mexico (exc. C), including 1 endemic each in Sin and Ver; Cipura 2 spp. Jal and SLP S to Chp and SE to Yuc; Dietes 2 spp. intro Chi, Dgo, NL S to Ver; Eleutherine 1 sp. native Hgo, Tab, Ver; Iris 7 spp. native and most of Mexico; Larentia 2 spp. endemic W and S Mexico; Libertia 1 SAM sp. intro to Oax; Nemastylis 1 sp. native widespread N and C Mexico S to Pue; Orthrosanthus 2 spp. native to Chp, Gto, Oax, and SLP; Sisyrinchium 24 spp. widespread N to S Mexico, less common in Cam, QR, and Yuc; Tigridia ~50 spp. native throughout Mexico, a few widespread, many restricted endemics; Trimezia 3-6 spp. native to C and S Mexico, NL, and Sin.

Neotropical Genera Include:

Crocoideae: Chasmanthe 1 sp. intro NE Argentina; Crocosmia 1 sp. intro Honduras, Hispaniola, Colombia, Venezuela, Bolivia, and NE Argentina; Freesia 1 sp. intro NE Argentina; Gladiolus 1-2 spp. intro to Jamaica, Peru, and NE Argentina; Romulea 1 sp. intro C Chile and NE Argentina; Sparaxis 1 sp. intro NE Argentina. Iridoideae: Alophia 3 spp. native to most of CAM, Guyana, Bolivia, and Brazil, including 2 endemic to Brazil; Calydorea 21 mostly SAM-endemic spp. of Colombia, Venezuela, Brazil, Bolivia, Paraguay, Uruguay, C. Chile, and NW Argentina; Cipura 10 spp. native to CAM, Antilles, and tropical SAM, excluding Ecuador, Guyana, and Suriname; Cobana monospecific CAM endemic to Guatemala and Honduras; Cypella 35 SAM-endemic spp. widespread in Peru, Bolivia, Brazil (exc. N), Paraguay, Uruguay, and NW Argentina; Dietes 1 sp. intro Jamaica; Eleutherine 3 spp. native to West Indies, N CAM, N+W SAM, Bolivia, Brazil, and Paraguay, including 2 SAM endemics; Ennealophus 6 spp. SAM endemic genus of Ecuador, Peru, N Brazil, Bolivia, and NW Argentina; Gelasine 8 spp. SAM endemic genus of Bolivia, Brazil, Uruguay, and NE Argentina; Herbertia 12 spp. former SAM endemics native to Colombia, Venezuela, Bolivia, N+C Chile, Paraguay, S Brazil, Uruguay, and N Argentina; Hesperoxiphion 5 spp. W SAM endemic genera of Colombia, Bolivia, and Peru; Iris 1-2 spp. intro Venezuela, Antilles, El Salvador, and NE Argentina; Larentia 1 SAM endemic sp. of Venezuela, Brazil, Bolivia, and Paraguay; Libertia ~12 spp. native and endemic from Colombia to Bolivia and Juan Fernández Is. and C Chile; Mastigostyla 29 spp. endemic genera of Andean SAM Puru, Bolivia, N Chile, and NW Argentina; Nemastylis 1 sp. native Guatemala and Honduras; Neomarica 1 sp. (unplaced most genus transferred to Trimezia) endemic to E Brazil; Olsynium 17 SAM endemic spp. mostly of Andean SAM in Peru, Bolivia, Chile, Argentina, and Colombia, but some may be restricted to the Patagonia region; Orthrosanthus 5 spp. native to most of CAM, Colombia, Ecuador, Venezuela, Peru, NW Argentina, and Bolivia, mainly high elevations; Sisyrinchium ~100+ spp. native to CAM, Cuba, and all of SAM excluding French Guyana and Suriname; Solenomelus 1 sp. endemic to C Chile; Tigridia ~10-20 spp. native to N CAM, Peru, and C Chile; Trimezia 77 spp. total natives to Mexico south through CAM and most of N SAM south to NE Argentina, with many in the highlands of Brazil, Venezuela, and Guyana.

Patagonia Genera Include:

Iridoideae: Calydorea 1 sp. from Coquimbo just N of the region to Bio Bio at the N limit of the region; Libertia 5 spp. throughout C & S Chile, S Argentina, and Juan Fernandez Islands, with 3 restricted to Los Lagos, Chile; Olsynium 4-6 spp. throughout the Patagonia region S to Tierra Del Fuego, S Magallanes, and Falkland Islands; Sisyrinchium 4 spp. found throughout the region S to Magallanes, Chile, and Santa Cruz, Argentina; Solenomelus 1 sp. endemic to C Chile and S Argentina; Tapeinia 1 sp. endemic to S Chile in Bio Bio to Los Lagos, also in S Magallanes and S Argentina.  

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.
• 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.
• 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 (2026): 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. I am also looking to invest in a new macro lens, as I will soon be adding floral dissections to some of the families. Donate to 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 Willis, Lyrae (2020+). Lyrae’s Nature Blog – Plant Families of North America. https://lyraenatureblog.com/