EUPHORBIACEAE

Weakley, Alan S., Poindexter, Derick B., Medford, Hannah C., Franck, Alan R., Bradley, Keith A., Sadle, Jimi & Kelley, John Michael, 2021, Studies In The Vascular Flora Of The Southeastern United States. Vii, Journal of the Botanical Research Institute of Texas 15 (1), pp. 23-56 : 32-33

EUPHORBIACEAE

Euphorbia : A new species of Euphorbia subgenus Chamaesyce from southern Florida, and a new name. Primary authors:Keith A.Bradley and Jimi Sadle

Reevaluation of Euphorbia porteriana in southern Florida rockland ecosystems indicates that three species should be recognized. Euphorbia hammeri is described as a new species endemic to the Everglades region of the southern Florida mainland. Its geographic isolation and rarity resulted in it being overlooked. It is partly sympatric with Euphorbia porteriana , which is endemic to Miami-Dade County. A new name is required for the Florida Keys endemic Chamaesyce scoparia Small , recognized now as Euphorbia ogdenii .

Florida, particularly southern peninsular Florida and the Florida Keys , is a hotspot of endemism in Euphorbia , subgenus Chamaesyce , sect. Anisophyllum , subsect. Hypericifoliae.Seven taxa from sect. Anisophyllum are endemic to Florida, six of which are entirely restricted to the extreme southern portion of the state ( Berry et al. 2016; Weakley 2020; Wunderlin et al. 2021). Among the endemics, a E. porteriana (Small) Oudejans species complex is distinguished from similar species in the area by having glabrous capsules, cyathia that are solitary in the leaf axils, mostly entire leaf margins, and inconspicuous united stipules. Euphorbia porteriana is morphologically most similar to the endemic E. garberi Engelm. ex Chapm. , a Federally Threatened species. Herndon (1993) clarified the distinction of E. garberi from E. porteriana (both as Chamaesyce ), which were confused by Burch (1965, 1966). Herndon treated all specimens that have uniformly pubescent capsules and usually pubescent foliage as E. garberi . This broadened concept of E. garberi includes C. adicioides Small , C. brachypoda Small , C. mosieri Small , and C. keyensis Small (none transferred to Euphorbia ), which we follow, as do others (Wunderlin & Hansen 2011; Berry et al. 2016; Weakley 2020). Yang and Berry (2011) placed E. porteriana and E. garberi in a “ Euphorbia serpens species complex” and hypothesized that the species, as well as E. blodgettii , are derived from E. serpens (Kunth) Small , and that E. porteriana and E. garberi are derived from hybridization events involving E. serpens and several other taxa, possibly including E. dioeca and E. deltoidea .

Small (1903) described C. porteriana based on a specimen collected in Miami, Miami-Dade County (Garber s.n., NY) and later considered it to be endemic to the county ( Small 1933). In addition, Small (1913) described C. scoparia Small from a specimen collected on Big Pine Key, Monroe County (Small 3819, NY) and considered that species to be endemic to the Florida Keys in the county ( Small 1933). In a Caribbean-wide treatment of Chamaesyce, Burch (1965) considered C. scoparia to be a variety of C. porteriana , endemic to the Florida Keys , and he later published the combination C. porteriana var. scoparia (Small) Burch ( Burch 1966) . Burch (1965, 1966) considered C. porteriana var. porteriana to be in both Miami-Dade County and the Florida Keys but his concept of var. porteriana included pubescent plants that represent C. garberi ( Herndon 1993) . Herndon treated all glabrous plants in both Miami-Dade County and the Florida Keys as one species, C. porteriana , and considered C. scoparia , with narrower leaves, to be a weakly differentiated form. This treatment has been followed by Wunderlin andd Hansen (2011), Berry et al. (2016), and Weakley (2020).

In 1978, a specimen of Chamaesyce ( Black & Black 203, FNPS, FTG) was collected in the Big Cypress National Preserve in an area known as the Lostman’s Pines region, in mainland Monroe County ( Avery & Loope 1980). A subsequent collection was made in 1979 (Rochefort 100, FNPS). The specimens were labeled as C. porteriana Small and as C. porteriana var. scoparia (Small) Burch by the collectors. These represent the first collections of any C. porteriana s.l. from mainland Monroe County or elsewhere in southwest Florida. The first author examined one specimen ( Black & Black 203, FTG) in the early 1990s and recognized that it differed from C.porteriana s.l. in having extremely long, narrow leaves as well as deep red cyathia, capsules, and stems. The long narrow leaves resembled some specimens of C. porteriana from the Florida Keys , but far exceeded the length and proportions of any other specimens. The late George N. Avery described observing this taxon in his unpublished field notes from the same area in 1981 (archived at Fairchild Tropical Botanic Garden, Coral Gables, Florida). No other documentation of C. porteriana s.l. from this region has been found by the authors.

In the early 2000s, during field work in the Lostman’s Pines region in the vicinity of the original collections, the taxon was rediscovered at several stations separated by as much as 7 km. In 2004, the second author estimated an overall population of 1,001 –10,000 individuals from Lostman’s Pines. All individuals showed the distinctive leaf dimensions and red pigmentation. In 2017, the second author discovered a population of Chamaesyce with the same characteristics in the Long Pine Key region of Everglades National Park in Miami-Dade County, approximately 50 km southeast of the Lostman’s Pines populations. An estimated 1,000 plants were observed in a 4-ha area. This population was growing within 100 m of C. porteriana with typical morphology and within the same pine rockland habitat type, but the two taxa were not found growing intermixed.

The distinctive features of this taxon, in both field observations and examination of specimens and the consistency of these characters between disjunct occurrences, indicated that the taxon was probably undescribed and related to C. porteriana and C. scoparia . Long-term field study of C. porteriana s.l. in Miami-Dade County and the Florida Keys indicated that the difference between mainland and Florida Keys populations should also be reevaluated to determine the most appropriate treatment of those taxa as well.

There has been a trend to treat Chamaesyce in a broadly circumscribed Euphorbia based on phylogenetic data (Steinmann & Porter 2002; Bruyns et al. 2006; Yang & Berry 2011; Yang et al. 2012; Berry et al. 2016). Some authors follow the broad treatment with reservations (Weakley 2020). In this work we adopt the broad concept of Euphorbia .

All specimens of E. porteriana s.l. were borrowed from FNPS, FTG, NY, and USF, including the type specimens. Ninety-six specimens were studied, including 44 of E. porteriana , 43 of E. ogdenii , and nine of E. hammeri . Length and width were measured from three representative mid-stem leaves on each sheet. Gland and gland appendage length (lateral dimension) and width (radial dimension) were also measured. Overall leaf shape, including base and apex shape, was recorded, as was the number of veins (midrib and secondary veins) visible in each leaf.The color of leaf veins, stems, glands, gland appendages, and capsule was recorded. Pedicels of mature capsules were characterized qualitatively as slender or stout. Measurements were also made of pickled specimens of E.porteriana and E. hammeri . Quantitative measurements show consistent differences in leaf shape and size between the three taxa ( Fig. 5 , Table 2). The three taxa were also found to be consistently separable by several other qualitative characters ( Table 2).

Based on quantitative and qualitative characters we conclude that this complex consists of three taxa best treated as species: E. porteriana is endemic to Miami-Dade County, E. ogdenii (= C. scoparia ) is endemic to the Florida Keys (requiring a new name if treated, as here, in Euphorbia ), and E. hammeri is a previously undescribed species that we circumscribe here. We name this species in honor of our friend Roger L. Hammer of Homestead, Florida, naturalist, author, and photographer, who has spent his life sharing his love of natural Florida with others.

Figures

FIG. 5. Leaf length-to-width ratios of Euphorbia taxa.