Zornia J.F.Gmel., Syst. Nat.

Zornia J.F.Gmel., Syst. Nat. View in CoL , ed. 13 [bis] 2(2): 1076, 1096. 1791 [1792], non Zornia Moench., Methodus 410. 1794, nom. illeg. superfl.

Type: Zornia bracteata J.F.Gmel.

Myriadenus Desv., J. Bot. Agric. View in CoL 1: 121. 1813. Type: Myriadenus tetraphyllus (L.) Desv.

Shrub 20 cm to 2 m tall. Stems erect, decumbent or prostrate, branched or not, glabrous to pubescent. Leaves with 2–4 leaflets, sessile, subsessile or petiolate, 2–66 × 0.5–20 mm, linear to orbicular, pubescent to glabrous. Stipules linear to ovate, 1–10 veined. Flowers papilonaceous, solitary or inflorescences spiciform, axillary or terminal, to 50 cm long; corolla yellow, usually with details in orange or red; bracteoles 3–20 × 1–10 mm, linear to ovate, 1–11 veined, punctate or not, sericeous to glabrous, red or green. Fruit a loment, with 2–15 articles; articles 1–7 × 1–5 mm, reticulate-veined or not, bristle-like trichomes 0.5–3.5 mm long or absent.

Etymology: Johannes Zorn (1739–1799) was a German pharmacist, botanist, and botanical illustrator. Zorn published six volumes of Icones plantarum medicinalium, illustrating and describing over 600 medicinal plants. The genus Zornia was named in his honor ( Brummitt & Powell, 1992).

Ecology and economic importance: Some Neotropical species of Zornia have pharmacological uses, such as Zornia brasiliensis Vogel with molluscicidal and anti-tumor activity ( Costa et al., 2015; David et al., 2007), and Zornia latifolia Sm. with anticonvulsant activity ( Alloisio et al., 2022; Cornara et al., 2018). Despite these promising findings, further research is needed to explore the chemistry of other species within the genus. Additionally, like many other species in the Papilionoideae subfamily, Zornia is commonly used as forage for livestock ( Polhill, 1994).

Distribution and habitat: Together the 50 Neotropical species of Zornia occur across the entire region. Notably, a center of diversity for the genus is in Brazil, with 37 species ( Fig. 2 View Figure 2 ). Furthermore, it is evident that Zornia exhibits significant levels of endemism, with 22 species exclusively occurring within their respective countries: Brazil (15 spp.), Mexico (4 spp.), Paraguay (1 sp.) and Venezuela (2 spp.).

The species occur within a wide range of biomes and vegetation types across the Neotropics, including Tropical Dry Forests, Savannas, Tropical Moist Forests, Montane Grasslands, and Temperate Grasslands ( Dinerstein et al., 2017). But, even within Tropical Moist Forests, the species generally prefer dry habitats, as evidenced by their occurrence in campinarana vegetation in the Amazon. This suggests that Zornia species are well adapted to dry environments ( Fig. 3 View Figure 3 ). As such, the genus could serve as a key model to understand the ecology and evolution of the dry environments existent in the Neotropics as a whole ( Dinerstein et al., 2017).

Conservation Status: Nine species were found to be Endangered (18%), 15 are considered Vulnerable (30%), 11 Near Threatened (22%), and only three species were considered of Least Concern. Twelve species (24%) are Data Deficient.

Overall, the data suggests a notable level of concern for a significant number of the Zornia species in the Neotropics. The high percentage of Data Deficient species also underscores the importance of ongoing research to fill knowledge gaps and inform effective conservation strategies. All this, combined with the fact that Neotropical Dry Forests and associated areas are under serious threat (DRYFLOR et al., 2016), highlights the urgency of carrying out studies like this one, which focus on the taxonomy and ecological aspects of groups intrinsically associated with these environments.

Notes: The species treated in this study can be distinguished by a combination of floral characteristics (such as solitary flowers vs. spiciform inflorescences) and leaflet morphology (tetrafoliolate vs. bifoliolate). When the flowers are arranged in inflorescences, they vary by being axillary or terminal. The bracteoles are also key morphological characters, varying in shape, indumentum, and whether they are punctate or not. For example, Zornia fimbriata Mohlenbr. is the only species in this study with non-punctate bracteoles, while Zornia flemmingioides Moric. is the only one with red-colored bracteoles ( Fig. 7C View Figure 7 ). Additionally, fruit morphology is an important feature for species differentiation ( Fig. 4 View Figure 4 ; Fortuna-Perez et al., 2015), with loment articles either having bristle-like trichomes or being smooth, and the surface either showing or lacking a reticulate-veined pattern.

In this study, Zornia echinata Mohlenbr. and Z. crinita (Mohlenbr.) Vanni were re-established. Also, second-step lectotypifications were made for Zornia lasiocarpa Ant. Molina and Z. thymifolia Kunth. Together with these nomenclature changes, our taxonomic study is the most comprehensive on Zornia for the Neotropical region to date.

To aid in more accurate identification, we provide here two identification keys that differentiate species based on the number of leaflets (bifoliolate vs. tetrafoliolate leaves).

Identification key to the tetrafoliolate species of Zornia in the Neotropics

1. Flowers solitary ................................................................................................................................................................. 2

1’. Flowers in spiciform inflorescences ................................................................................................................................. 3

2. Loment with 15 articles, bristle-like trichomes absent ............................................................................... Z. myriadena

2’. Loment with up to 10 articles, bristle-like trichomes present ................................................................. Z. echinocarpa

3. Loment with bristle-like trichomes absent ..................................................................................................................... 4

3’. Loment with bristle-like trichomes present ................................................................................................................... 8

4. Bracteoles red-colored .............................................................................................................................. Z. flemmingioides

4’. Bracteoles green-colored .................................................................................................................................................. 5

5. Bracteoles obovate ............................................................................................................................................. Z. mitziana

5’. Bracteoles oblong ............................................................................................................................................................. 6

6. Leaflets linear .................................................................................................................................................. Z. harmsiana

6’. Leaflets ovate to obovate ................................................................................................................................................. 7

7. Stems with a villous indumentum; inflorescence approx. 7 cm long; bracteoles with a villous indumentum .... Z. ulei

7’. Stems with a hirsute indumentum; inflorescence approx. 20 cm long; bracteoles with a pilose indumentum ............. .................................................................................................................................................................................. Z. glaziovii

8. Occurring in Temperate Grasslands of North America .................................................................................. Z. bracteata

8’. Occurring in Tropical Dry Forests and Savannas of South America .............................................................................. 9

9. Leaves sessile or subsessile ............................................................................................................................. Z. subsessilis

9’. Leaves petiolate .............................................................................................................................................................. 10

10. Stems prostrate to decumbent ...................................................................................................................................... 11

10’. Stems erect ................................................................................................................................................................... 12

11. Stipules lanceolate; bracteoles elliptic, strigose ........................................................................................ Z. brasiliensis

11’. Stipules ovate; bracteoles ovate, glabrous ..................................................................................................... Z. cearensis

12. Loment with 2–3 articles, bristle-like trichomes 3.5 mm long. ...................................................................... Z. virgata

12’. Loment with 3–6 articles, bristle-like trichomes up to 1.5 mm long ........................................................................ 13

13. Bracteoles ovate, 7–13 veined ................................................................................................................... Z. gardneriana

13’. Bracteoles elliptic, 4–7 veined ..................................................................................................................................... 14

14. Inflorescence up to 15 cm long; loment not reticulate-veined ................................................................ Z. guanipensis

14’. Inflorescence up to 25 cm long; loment reticulate-veined .......................................................................... Z. tenuifolia

Identification key to the bifoliolate species of Zornia in the Neotropics

1. Loment with bristle-like trichomes absent ..................................................................................................................... 2

1’. Loment with bristle-like trichomes present ................................................................................................................... 7

2. Stems not branched .................................................................................................................................... Z. melanocarpa

2’. Stems branched ................................................................................................................................................................ 3

3. Bracteoles ovate; occurring in North America ................................................................................................................. 4

3’. Bracteoles elliptic; occurring in South America .............................................................................................................. 5

4. Stipules elliptic, 3–5 veined ................................................................................................................................... Z. laevis

4’. Stipules linear, 1 veined ................................................................................................................................ Z. sinaloensis

5. Inflorescence spiciform terminal, 30 cm long ................................................................................................... Z. pardina

5’. Inflorescence spiciform axillary, 20 cm long ................................................................................................................... 6

6. Leaflets ovate to elliptic, strigose ................................................................................................................... Z. hebecarpa

6’. Leaflets ovate to lanceolate, tomentose ........................................................................................................ Z. ramboana

7. Inflorescence spiciform, terminal ..................................................................................................................................... 8

7’. Inflorescence spiciform, axillary .................................................................................................................................... 11

8. Loment reticulate-veined ................................................................................................................................. Z. burkartii

8’. Loment not reticulate-veined .......................................................................................................................................... 9

9. Loment articles with bristle-like trichomes 1.5 mm long .................................................................................. Z. sericea

9. Loment articles with bristle-like trichomes 2 mm long ................................................................................................ 10

10. Stems decumbent and glabrous ..................................................................................................................... Z. echinata

10’. Stems erect and velutinous ........................................................................................................................ Z. cryptantha

11. Stems not branched ....................................................................................................................................... Z. decussata

11’. Stems branched ............................................................................................................................................................ 12

12. Stems decumbent or prostrate ..................................................................................................................................... 13

12’. Stems erect ................................................................................................................................................................... 21

13. Loment not reticulate-veined ....................................................................................................................................... 14

13’. Loment reticulate-veined ............................................................................................................................................. 17

14. Loment articles with bristle-like trichomes up to 0.5 mm long ................................................................... Z. herbacea

14’. Loment articles with bristle-like trichomes 1 mm long ............................................................................................. 15

15. Leaflets orbiculate ......................................................................................................................................... Z. orbiculata

15’. Leaflets ovate to lanceolate .......................................................................................................................................... 16

16. Stipules elliptic to lanceolate, 7–9 veined; bracteoles elliptic, sericeous ........................................................ Z. crinita

16’. Stipules obovate to lanceolate, 5–7 veined; bracteoles ovate, glabrous ............................................... Z. multinervosa

17. Inflorescence spiciform, 30 cm long ................................................................................................................ Z. curvata

17’. Inflorescence spiciform, up to 15 cm long .................................................................................................................. 18

18. Bracteoles elliptic to lanceolate ................................................................................................................. Z. microphylla

18’. Bracteoles ovate ............................................................................................................................................................ 19

19. Bracteoles with a glabrous indumentum ..................................................................................................... Z. thymifolia

19’. Bracteoles with a sericeous indumentum ................................................................................................................... 20

20. Loment with 6–8 articles; articles 2 × 2 mm; occurring in Montane Grassland and Savanna of South and Central America ................................................................................................................................................................... Z. contorta

20’. Loment with 3–4 articles; articles 3–3.2 × 3–3.4 mm; occurring in Tropical Dry Forest of North America ............... .......................................................................................................................................................................... Z. megistocarpa

21. Loment not reticulate-veined ....................................................................................................................................... 22

21’. Loment reticulate-veined ............................................................................................................................................. 23

22. Leaflets filiform; bracteoles linear-lanceolate, 3–4 veined, glabrous ........................................................... Z. filifoliola

22’. Leaflets ovate to elliptic; bracteoles elliptic, 5–7 veined, strigose ................................................................. Z. confusa

23. Loment with bristle-like trichomes 3.5 mm long .................................................................................... Z. trachycarpa

23’. Loment with bristle-like trichomes up to 2 mm long ................................................................................................ 24

24. Stems glabrous .............................................................................................................................................................. 25

24’. Stems pubescent to villous .......................................................................................................................................... 32

25. Inflorescence spiciform, up to 15 cm long ................................................................................................................... 26

25’. Inflorescence spiciform, 30–40 cm long ..................................................................................................................... 29

26. Bracteoles linear ............................................................................................................................................................ 27

26’. Bracteoles ovate ............................................................................................................................................................ 28

27. Stipules elliptic; loment with 2–3 articles ................................................................................................... Z. lasiocarpa

27’. Stipules linear to lanceolate; loment with 3–7 articles ............................................................................ Z. leptophylla

28. Inflorescence spiciform 10 cm long; occurring in Mexico............................................................................... Z. venosa

28’. Inflorescence spiciform 15 cm long; occurring in Peru and Ecuador.......................................................... Z. piurensis

29. Stipules lanceolate ........................................................................................................................................................ 30

29’. Stipules elliptic ............................................................................................................................................................. 31

30. Bracteoles 11–14 × 5–6 mm, ovate–lanceolate, 5–7 veined; loment with articles 1.5–2 × 1.5–2 mm .......... Z. glabra

30’. Bracteoles 5–12 × 2–4 mm, linear, 3–6 veined; loment with articles 2–3 × 2–2.5 mm ............................... Z. latifolia

31. Bracteoles 6–9 × 2–3 mm ............................................................................................................................. Z. vichadana

31’. Bracteoles 10–15 × 5–7 mm ......................................................................................................................... Z. reticulata

32. Bracteoles not punctate ................................................................................................................................. Z. fimbriata

32’. Bracteoles punctate ...................................................................................................................................................... 33

33. Bracteoles lanceolate and villous ........................................................................................................................ Z. villosa

33’. Bracteoles ovate and glabrous ..................................................................................................................................... 34

34. Inflorescence spiciform 3 cm long; loment with 5–6 articles; articles 2 × 1.5–2 mm ............................. Z. grandiflora

34’. Inflorescence spiciform 10 cm long; loment with 4–5 articles; articles 2–3.5 × 2.5–3 mm ........................ Z. afranioi