Crassula × mortii Gideon F.Sm. & N.R.Crouch

Smith, Gideon F. & Crouch, Neil R., 2021, Crassula × mortii (Crassulaceae subfam. Crassuloideae), a new natural hybrid between C. perforata and C. rubricaulis from South Africa’s southern Cape, Phytotaxa 487 (1), pp. 97-102 : 97-98

Crassula × mortii Gideon F.Sm. & N.R.Crouch , nothosp. nov. ( Fig. 2A–D ).

Type: — SOUTH AFRICA. Western Cape province, 3322 (Oudtshoorn): Montagu Pass , cremnophytic on sandstone cliff, alt. 350 m, (–CD), 6 December 2019, flowered in cultivation in Pretoria during October 2020, N. Crouch 1298 (holotype PRU!) .

Parentage: — Crassula perforata Thunberg (1778: 329 , 338) × Crassula rubricaulis Ecklon & Zeyher (1837: 296) .

Diagnosis: —Vegetatively C. × mortii differs from C. perforata by having more elliptic, dull khaki green leaves, rather than somewhat deltoid, glaucous leaves. The leaf margins are ciliate in C. × mortii, as in C. rubricaulis , rather than horny as in C. perforata . Crassula × mortii differs from C. rubricaulis by not having cultrate to oblanceolate leaves, and the leaves of C. × mortii are basally fused, as in C. perforata , rather than free as in C. rubricaulis . The flowers of C. × mortii are bright white, as in C. rubricaulis , not cream to pale yellow as in C. perforata , and of an intermediate size. The sepals of C. × mortii are bluntly acute as in C. perforata , not sharply acute as in C. rubricaulis , and have margins smooth rather than minutely toothed, as often found in C. rubricaulis . Crassula × mortii flowers earlier than either of its parents and has 6- rather than 5-partite floral parts.

Description: —Perennial, branched, small to medium-sized, pendent, somewhat spreading, succulent shrublets to 30 cm tall and wide. Roots fibrous, often produced at nodes where stem touches the soil. Stems 3–4 mm in diameter, reddish when young, becoming woody, dark brown with age; bark reddish brown to dark brown, flaking. Leaves elliptic to ovate, often crowded towards the branch tips, old leaves persistent for a long time; blade (8–)10–15(–20) × 5–8(–12) mm, dull khaki green, often strongly red-infused, obscurely to distinctly red-spotted, flattened to concave adaxially, convex abaxially; margins red, ciliate; base cuneate, fused to opposite leaf in a pair; apex bluntly acute-tipped. Inflorescence small to mediumsized, few- to many-flowered, elongated to rounded thyrse with ± sessile flowers, brittle when dry; peduncle indistinct as a result of vegetative leaves grading into bracts higher up. Calyx consisting of 6 sepals; sepals (0.5–)1.0(–1.5) mm long, light green, longitudinally reddish brown-infused especially towards apex, drying reddish brown, elongated-triangular to narrowly oblong, basally very slightly fused, margins smooth, apex bluntly acute, mucronate. Corolla consisting of 6 petals, short-tubular, basally fused for ± 0.1 mm, uniformly bright white; lobes 3.0– 3.5 mm long, ovate-oblong, spreading at first, soon recurved, sometimes adorned with a minute abaxial appendage near apex. Stamens 6; filaments 1.5–2.0 mm long, white; anthers 0.50–0.75 mm long, mustard yellow, ± elliptic, well-exserted. Carpels 6, 1.0– 1.5 mm long, white, free, rather abruptly tapering into styles; styles ± 0.75 mm long, yellowish white; stigmas capitate, more intensely yellow than styles. Squamae 0.2–0.3 × 0.25–0.35 mm, whitish green, ± horizontally oblong, free, succulent. Follicles 3–4 mm long, drying blackish brown, dehiscent. Seed ± 0.5 mm long, light brown to reddish brown, with a rough surface, ellipsoid. Chromosome number unknown.

Distribution and habitat: — Crassula × mortii is currently known from a single location along Montagu Pass, which is located to the north of George in the Outeniqua Mountains of the Western Cape Province of South Africa, but it likely also occurs elsewhere where the natural geographical distribution ranges of its putative parents, C. perforata and C. rubricaulis , overlap. The nothospecies grows as a cremnophyte on a steep, semi-shaded, moist, west-facing sandstone rock face ( Fig. 2A ), alongside its putative parents and various other small succulents and geophytes. At the type locality the novelty finds purchase in shallow soil overlying a rock ledge, where it presents a pendulous habit ( Fig. 2A ).

Phenology: —Flowers ( Fig. 2B–C ) early- to mid-summer in the southern hemisphere.

Etymology: — Crassula × mortii is named for Mark Eugene Mort (born 25 May 1969, Seward, Pennsylvania, USA –) ( Fig. 2E ). Growing up in western Pennsylvania, very close to the Appalachian Mountains, Mark was able to explore nature from a young age. In 1992 he completed a BS degree in Biology at Indiana University of Pennsylvania, after which he was awarded a fellowship to study at the Mount Desert Island Biological Laboratory near Bar Harbor, Maine. Plant taxonomy became Mark’s primary interest as a Masters student at the College of William and Mary in Williamsburg, Virginia, where he conducted a floristic study of the vascular plants and forest vegetation in Prince George County, Virginia. In 1994 Mark graduated with a Master’s degree and then initiated his doctoral studies at Washington State University, Pullman, Washington. His dissertation included a broad molecular phylogenetic study of the family Crassulaceae based on chloroplast sequence data. He eventually published some of the earliest phylogenetic analyses of the Crassulaceae ( Mort et al. 2001, 2005a, b, 2009) and has a continuing interest in the family ( Smith et al. 2017). In the course of his research he conducted multiple collecting expeditions, including to the Canary Islands and South Africa, which enabled him to study diversity in the Old World Crassulaceae first-hand. Following the award in 1999 of a doctoral degree, he undertook postdoctoral work at Ohio State University. In 2001, he accepted a tenure-track position at the University Kansas in Lawrence, Kansas, in the Department of Ecology and Evolutionary Biology (assistant professor) and the Biodiversity Institute and Natural History Museum (Assistant Curator). Presently, Mark is a tenured full professor at the University of Kansas where he also serves as co-director for the Undergraduate Biology Program.

Discussion: —Morphological assessment of the taxon represented by N. Crouch 1298 (PRU) revealed it to not correspond with any known Crassula species from southern Africa, but rather to represent a hybrid, here named C. × mortii, based on putative parents found growing sympatrically at Montagu Pass. The form of both vegetative and reproductive characters was intermediate in many respects with C. perforata and C. rubricaulis ( Fig 1E ; Table 1 ). Crassula rubricaulis was included in C. sect. Curtogyne ( Haworth 1821: 8) Tölken (1977a: 300) , corresponding to sect. XII of Tölken (1985: 158–159), while C. perforata was included in C. sect. Perfilatae Haw. ex De Candolle (1828: 18) (see Tölken 1977b: 410, Tölken 1985: 189– 190 [sect. XV]). That the nothospecies is of intersectional origin is consistent with observations by Tölken (1977a: 301) that species in C. sect. Curtogyne can hybridise beyond sectional limits, particularly with some in C. sect. Squamulosae Haworth (1821: 11). This report, however, represents the first record known to us of a hybrid involving C. rubricaulis as a parent, and of hybridisation between C. sect. Curtogyne and C. sect. Perfilatae, as defined by Tölken (1977a, b, 1985). However, neither C. sect. Curtogyne nor C. sect. Perfilatae is monophyletic according to Bruyns et al. (2019).

Figures

FIGURE 1.A. Crassula perforata habit, with leaf pairs basally fused. B. Crassula perforata inflorescence. C. Crassula rubricaulis habit with leaves basally cuneate. D. Crassula rubricaulis inflorescence. E. Leafy shoots of C. perforata (left), C. ×mortii (centre), and C. rubricaulis (right), all from Montagu Pass. Scale bars:A: 7 cm; B: 9 mm; C: 45 mm; D 4.5 mm; E: 8 mm. Photographs: Neil R. Crouch.

FIGURE 2. Crassula ×mortii from Montagu Pass, Western Cape Province, South Africa. A. Habit. B. Inflorescence lateral view. C. Inflorescence dorsal view. D. Leafy shoot. E. Mark Mort (1969–) while conducting fieldwork in South Africa. Scale bars:A: 30 mm; B: 3 mm; C: 3 mm; D 7 mm. Photographs by the authors (A–D) and Jenny Archibald (E).