Euphorbia thymifolia Linnaeus, Sp. Pl.

Mugnai, Michele, Lazzaro, Lorenzo, Nuzzo, Luca Di, Foggi, Bruno, Viciani, Daniele & Ferretti, Giulio, 2021, Synopsis of Euphorbia section Anisophyllum (Euphorbiaceae) in Italy, with an insight on variation of distribution over time in Tuscany, Phytotaxa 485 (1), pp. 1-65 : 42-47

17. Euphorbia thymifolia Linnaeus, Sp. Pl. 1: 454. 1753.

Type (lectotype, designated by Wheeler 1941: 253):— [ INDIA]. Herb. Linn. 630.10 ( LINN image!)

≡ Anisophyllum thymifolium (L.) Haworth (1812: 160)

≡ Chamaesyce thymifolia (L.) Millspaugh (1916: 412)

Description:—Herbs, annual or perennial, with taproot. Stems prostrate, mat-forming, 15–30 cm, strigose. Leaves opposite; stipules distinct or slightly connate at base, linear-subulate, 0.9–1.2 mm, strigose-tomentulose; petiole 0.5– 1.0 mm, sparsely strigose; blade broadly elliptic to ovate-lanceolate, 3–10 × 1.8–5.0 mm, base asymmetric, margins serrate to serrulate, apex blunt to acute, abaxial surface sparsely tomentulose to glabrate, adaxial surface glabrate; palmately veined at base, pinnate distally. Cyathia usually in small, cymose clusters on congested, axillary branches; peduncle (0–) 0.1–0.3 mm. Involucre broadly obconic, becoming distended and distorted by base of partially included capsule, 0.4–0.8 × 0.3–0.5 mm, strigose; glands 4, red, subcircular to oval, 0.1–0.2 × 0.2–0.3 mm; appendages white to pink, sometimes rudimentary, 0.1–0.4 × 0.1–0.3 mm, margin entire or crenulate. Staminate flowers 3–5. Pistillate flowers: ovary densely strigose; styles 0.4–0.5 mm, 2-fid ½ length. Capsules conic to truncate-ovoid, scarcely exserted from involucre, base often remaining inside involucre and splitting one side of it during maturation, 0.9–1.2 × 1.0– 1.2 mm, sparsely to moderately strigose; columella 0.6–1.0 mm. Seeds with white coat, testa tan brown, ovoid to narrowly ovoid, sharply 4-angled in cross section, 0.8–0.9 × 0.4–0.6 mm, with 4 low transverse ridges often slightly extending into angles, not sulcate.

Iconography:—Fig. 29.

Chromosome number:—2n = 18 (Krishnappa & Reshme 1982); n = 9 ( Hans 1973); 2n = 19 ( Hsu 1967); 2n = 20 ( Chopde 1965).

Ecology:—Accidentally dispersed by humans as contaminant; globally considered as weed of cereals, orchards and plantations. The species occurs in disturbed areas, often near salt water ( Steinmann et al. 2016).

Alien status:—Neophyte native to the New World, recorded by mistake in Italy ( Galasso et al. 2018b).

Occurrence in Italy:—Absent. Recorded by mistake in VDA, LIG, TOS and LAZ.

Taxonomic annotations:—Many authors (e.g. see below) cited this species adopting the name Euphorbia thymifolia Burm. , referring to the description in Burman (1768: 112). Nevertheless, we could verify that Burman itself based his description on the former name by Linnaeus (“Linn. Sp. 651”, which corresponds to E. thymifolia in the second edition of the Species Plantarum, see Linnaeus 1762). Thus, it is reasonable that he was not formalizing a new name. Accordingly, Euphorbia thymifolia Burman should be considered as a name misapplied by following authors. Euphorbia thymifolia was recorded for the first time in Italy for TOS under the name E. thymifolia Burm. by Arcangeli (1894), and subsequently by Chiovenda (1895) for LAZ and by Sommier (1898) for VDA. The presence in LIG was based on historical records ( Galasso et al. 2018a; specimens preserved in FI! and RO!, see Appendix 1). Many authors stated that all Italian records of E. thymifolia were erroneous and correspond to E. maculata ( Galasso et al. 2018b) . The two species are generally similar but E. thymifolia is easily recognizable by the non-exserted capsule that at maturity remain largely enclosed by the involucre, and by its unequal involucral gland appendages ( Steinmann et al. 2016).

Type designation:— Steinmann & Felger (1997) stated that Linnaeus specimens should be considered as holotype material (further adding that the specimen comes from India). Nevertheless, according to Jarvis (2007), Linnaeus’ specimen (630.10 LINN) was designated as the lectotype of E. thymifolia L. by Wheeler (1941). However, it should be noted here that Wheeler (1941) himself posed doubts concerning the correspondence between the type in LINN and its appplication. Later, also Burch (1965) doubted that the exsiccata by Linnaeus correspond to E. thymifolia rather than E. maculata , in agreement with the doubts expressed by James Edward Smith on the sheet (“ maculata ? ”). In addition, Burch concerned that the current use of the name E. thymifolia may be different from Linnaeus interpretation, and that there is not certainty whether Linnaeus ever saw the plant to which his name is usually applied. We analyzed the image of the specimen but, unfortunately, we were not able to verify its identification, nor to find clear evidences that the interpretation of Wheeler should be considered incorrect. We note here that further in-deep researches are needed to clarify whether the current application of this name is correct.

Identification key to Euphorbia sect. Anisophyllum (Euphorbiaceae) in Italy

1. Ovaries and capsules glabrous............................................................................................................................................................2

– Ovaries and capsules ± hairy............................................................................................................................................................11

2. Cyathia grouped in dense glomerules; stems erect or ascending; leaves> 1.3 cm long....................................................................3

– Cyathia not grouped in dense glomerules; stems prostrate; leaves ≤ 1.3 cm long.............................................................................5

3. Stems and leaves glabrous; seeds with light brown testa ............................................................................................ E. hypericifolia

– Stems and leaves sparsely pilose; seeds with blackish testa ..............................................................................................................4

4. Stems distally pubescent, at least in lines on the stem side; seeds irregularly wrinkled; stipules 1.0– 1.5 mm .................... E. nutans

– Stems distally glabrous; seeds with 2–3 transverse ridges; stipules 0.7–0.9 mm ........................................................ E. hyssopifolia

5. Seeds smooth......................................................................................................................................................................................6

– Seeds ornamented...............................................................................................................................................................................9

6. Seeds> 2.5 mm long; leaves curved with manifest basal auricles......................................................................................... E. peplis

– Seeds ≤ 1.3 mm long; leaves straight without auricles ......................................................................................................................7

7. Leaves ovate to suborbicular, margin entire, apex retuse and stipules deltoid; seeds tetrahedral................................. 8 ( E. serpens )

– Leaves oblong to oblanceolate, margin dentate, apex rounded and stipules laciniate; seeds ovoid ................................. E. humifusa

8. Stipules connate; seeds smooth; 2n = 24..................................................................................................... E. serpens subsp. serpens

– Stipules distinct; seeds with shallow furrows or grooves; 2n = 44 ........................................................ E. serpens subsp. fissistipula

9. Leaves narrowly oblong to oblong-obovate; seeds with prominent transverse ridges that pass through the angles ........................... ................................................................................................................................................................................... E. glyptosperma

– Leaves ovate to obovate; seeds irregularly granulose-transversely rugose......................................................................................10

10. Glands yellowish; seeds cinereous-blackish ................................................................................................................ E. chamaesyce

– Glands purplish; seeds reddish .................................................................................................................................... E. engelmannii

11. Stems erect or ascending; cyathia not grouped in dense glomerules (except E. ophthalmica )........................................................12

– Stems prostrate; cyathia grouped in dense glomerules.....................................................................................................................16

12. Plant glabrescent with pubescence limited to distal stems, at least in lines on the stem side ............................................... E. nutans

– Plant pilose with diffused pubescence..............................................................................................................................................13

13. Leaf apex obtuse; blade margins entire to crenate or roundly serrate ..............................................................................................14

– Leaf apex acute; blade margins sharply serrate................................................................................................................................15

14. Glomerules of cyathia terminal; capsules with deep slits between carpels.................................................................... E. berteroana

– Glomerules of cyathia axillary; capsules without slits.......................................................................................................... E. indica

15. Glomerules of cyathia terminal and axillary, axillary glomerules sessile or at tips of elongated, leafless stalks; stems branching at base but only infrequently near tips......................................................................................................................................... E. hirta

– Glomerules of cyathia terminal, on main stems or short, leafy, axillary branches, with reduced, bractlike leaves subtending cyathia; stems branching freely................................................................................................................................................. E. ophthalmica

16. Capsules without uniform indumentum and patent hairs.................................................................................................................17

– Capsules with uniform indumentum and adpressed hairs ................................................................................................................18

17. Capsules with indumentum only on the keels; seeds transversely striate ........................................................................ E. prostrata

– Capsules with indumentum evenly spread; seeds irregularly granulose-rugose .......................................................... E. chamaesyce

18. Cyathia grouped in dense glomerules.......................................................................................................................... E. ophthalmica

– Cyathia not grouped in dense glomerules ........................................................................................................................................19

19. Seeds smooth or papillate; stems rooting at nodes......................................................................................................... E. humistrata

– Seeds with 3–4 transverse ridges; stems not rooting at nodes..........................................................................................................20

20. Capsules well exserted from involucre at maturity; leaf blade usually with irregular reddish streak along midvein .... E. maculata

– Capsules scarcely exserted from involucre, base often remaining inside involucre and splitting one side of it during maturity; leaf blade without reddish streak............................................................................................................................................ E. thymifolia

Temporal variation of distributions in Tuscany

As a result of our field and herbaria investigations, we collected a detailed information concerning the distribution of E. sect. Anisophyllum in Tuscany, and their abundance in the Tuscan Herbaria. The data collected allowed to update the species distribution and status of naturalization at province and regional scale. Eight taxa have been retrieved in Tuscany, but three of them resulted now not retrieved in many provinces (see Table 2). We searched for the occurrence of E. chamaesyce , E. humifusa , and E. nutans in historical sites of occurrence, and their current presence was not confirmed in most of cases. In particular, we accurately verified current the occurrence of E. chamaesyce in Arezzo and Siena provinces, and of E. nutans in Grosseto and Pistoia provinces. Euphorbia humifusa was not found in any of the sites where it had been historically recorded. In Table 2, we provide the update occurrence of species for each province. The current presence is based on field investigations and herbarium specimens collected from 1950 onwards.

TOS AR FI GR LI LU MS PI PT PO SI

Euphorbia chamaesyce + + + + 0 0 0 0 0 +

Euphorbia humifusa CAS CAS 0 0 0

Euphorbia hypericifolia CAS CAS

Euphorbia maculata INV INV INV INV INV INV INV INV INV INV INV

Euphorbia nutans NAT CAS 0 CAS 0 0 0 NAT

Euphorbia peplis + + + + + +

Euphorbia prostrata INV INV INV INV INV INV INV INV INV INV INV

Euphorbia serpens subsp. serpens NAT NAT NAT NAT NAT

Figure 30A reports a conditional density plot, showing the variation in abundance of records of the different species that have been retrieved in Tuscany since 1836. Temporal distribution of occurrences shows a decrease in records of E. chamaesyce , E. humifusa , and E. nutans , and an increase in records of E. prostrata and E. maculata . These results are consistent with empirical evidences of fluxes in densities of different species populations. Reduction of native ( E. chamaesyce ) and formerly colonizing species ( E. humifusa and E. nutans ) and increase of more recently colonizing ones ( E. prostrata and E. serpens ) is accordance with a general trend of increase in the number of alien species, particularly in anthropic contexts ( Galasso et al. 2018 a, Lososová et al. 2012, Celesti-Grapow et al. 2006). Euphorbia peplis is a peculiar species, considering that it grows in habitat subject to stable disturbances (coastal dunes), in contrast to highly variable disturbance typical of other habitats.

Results of data summarized for provinces and time intervals showed significant variations in species temporal distribution (Pearson’s chi-squared test had as result a p -value of 0.0388, figure 30B), confirming the trends showed in the conditional density plot. Furthermore, it is relevant how significance is not affected by the large amount of data at the turn of XX century, due to important Italian floras, and at the present day, due to our field investigations.