Aphyllon spectabile L.T.Collins, Velazco, & A.C.Schneid., sp. nov. Type: Mexico. Nuevo León: Santa Catarina, La Huasteca Park entrance, 21 Aug 2021, Carlos Velazco s.n. (holotype: MO).

Plants unbranched (excluding inflorescence), 7–27 cm. Stem base not or only slightly enlarged. Roots few to many, short, fragile, root mass poorly developed and less than 10 mm in diameter. Leaves several to numerous, lanceolate or broadly triangular, 3–10 mm, glabrous, margins entire, or sometimes ciliate. Inflorescences compact racemes, short or elongate, glandular-puberulent, rarely branched, pallid (sometimes entirely creamy-white) or purple tinged, bracts narrowly lanceolate to lanceolate, 11–20 mm, apex acute or acuminate, densely glandular-pubescent. Pedicels 0–5(10) mm, only proximal flowers pedicellate; bracteoles 2. Flowers: calyx (15)19–23 mm, slightly asymmetric, cup 4–5 mm, lobes 15–16 mm, reflexed, narrowly lanceolate-attenuate, pallid externally or purple tinged, purple internally, densely glandular pubescent; corolla 35–40 mm, tube white, pubescent externally, only slightly bent, mouth flared, abruptly constricted above ovary, purple veins in the lobes but not in the tube; palatal folds prominent, yellow, pubescent; abaxial (lower) lip 12–15 mm, lobes dark purple, lavender or white, rarely pale blue, apex obtuse or rounded, margins incurved or involute; adaxial(upper) lip 12–15 mm, erect or reflexed, dark purple, lavender, or rarely white, or pale blue, lobes erect or reflexed, sometimes torqued (bent) centripetally, rounded, margins entire, undulate or erose, pubescent or glabrous; filaments pilose, glabrous at insertion, anthers included, pilose; stigma peltate, discoid-crateriform or 2-lobed, sometimes with a descending narrow appendage. Fruit: Capsule. Flowering from Nov–May, most frequently in Feb and Mar. Figure 1C.

Diagnosis—Aphyllon spectabile can be distinguished from A. ludovicianum by its much larger flowers, narrow distribution range around Monterrey, Mexico, and the unique host species Gymnosperma glutinosum.

Distribution—Aphyllon spectabile is restricted to a small area in the Sierra Madre Oriental in northeastern Mexico, in the vicinity of Monterrey, Nuevo Leon, including Sierra de las Mitras, Sierra de la Sillas, and Sierra de la Loma Largo. A single specimen is reported from the adjacent state of Coahuila, with the location given only as “Saltillo.” Since the authors were not able to access other collections from the Sierra Madre Oriental, it is possible that the species is more widely distributed than indicated in this treatment.

Habitat—The species occurs in the zone of xeric vegetation (mattoral xerofila) primarily on arid and semiarid mountain slopes of the Sierra Madre elevations between 500 and 1500 m. This species is found in several different vegetation assemblages within this zone, whereas A. ludovicianum is primarily found in prairies.

Host—The only reported host species is Gymnosperma glutinosum Less. (Asteraceae), although the authors were not able to confirm this association by direct observation. Aphyllon was not previously known to parasitize Gymnosperma Less., but other members of the subtribe Gutierreziinae do serve as host species, including Gutierrezia Lag. (A. arizonicum, A. multiflorum), and Euthamia (Nutt.) Cass. (A. californicum subsp. grayanum (Beck) A.C.Schneid.; herbarium vouchers Colwell 14–25 at YM; Mason 12127, JEPS 20913).

Etymology—The epithet spectabile refers to the distinctively large and brightly colored flowers.

Phylogenetic Affinities—Phylogenetic evidence strongly supports the placement of A. spectabile within the A. ludovicianum complex, although existing markers are not sufficient to further resolve most species within this clade, nor provide support for or against species monophyly (Fig. 3).

Notes—Morphologically, several floral characters clearly differentiate Aphyllon spectabile from A. ludovicianum and other close relatives or co-occurring species (Table 1). The corollas of A. spectabile are 35–45 mm long, which is approximately double the size of the 14–20 mm long corollas of A. ludovicianum. Likewise, the corolla lobe lengths of A. spectabile (13–15 mm) are about twice as long as those of A. ludovicianum (5–8 mm long). Only the highly disjunct A. californicum has flowers this large, but the two species differ in floral architecture, biogeographic distribution, and host affinity (Tables 1, 2).

The corolla tube of A. spectabile is white with large purple lobes, purple veins, and measuring about 10 mm at the opening. This is noticeably different from A. ludovicianum, in which the tube is lavender, pinkish, or yellow, rarely pure white, with lobes similarly colored, without purple veins and measuring only about 5 mm at the opening. Additionally, the margins of lower corollas lobes are involute in A. spectabile, while the margins in A. ludovicianum are only slightly incurved.

Ecologically and biogeographically, Aphyllon spectabile and A. ludovicianum are also distinct. A. ludovicianum is a prairie species distributed throughout the North American Prairies to the eastern slopes of the Rocky Mountains. It utilizes a variety of host species, but is found primarily on Artemisia L. spp., Heterotheca Cass. sp., and Grindelia squarrosa (Pursh) Dunal, but never Gymnosperma.

Contrasted with the two previously mentioned species, A. multiflorum has intermediately sized corollas that are 22–36 mm long with lobes 5–9 mm long (Table 1). The distribution of A. multiflorum is in the arid grasslands and semi-desert of the southern plains in Colorado, New Mexico, and western Texas. The primary host is Gutierrezia sarothroe (Pursh) Britton & Rusby, but occasionally is found on Heterotheca spp.

The only other species that occurs with A. spectabile in the Sierra Madre in the vicinity of Monterrey, Mexico is Aphyllon cooperi A.Gray. However, several morphological characters distinguish these two taxa, most notably corolla and calyx measurements and corolla lobe differences (Table 2). Host and phylogenetic position are also highly distinct from A. spectabile (Fig. 3).

Additional Specimens Examined—Mexico. —Coahuila: Saltillo [no location or habitat data], 1–15 Apr 1880, E. Palmer s.n. (NY). NUEVA LEON: near Monterrey, 20 May 1900, Wm. Canby 183 (TEX). Monterrey, 3 Mar 1900, Trelease 183 (MO, GH). 5 miles SE of Monterrey, J.T.Bucholz s.n. (ILL). Corrizalejo, 3 miles out [from Monterrey?], 23 Mar 1946, Jose Roybal 48 (US). Monterrey, 20 Apr 1947, M.M. Lacas 266 (F). Monterrey, Obispado, 1 May 1947, M.M. Lucas 338 (F). Hillside, thorny vegetation, Monterrey, San Augustino, 22 Apr 1960, Robert F. Smith M125 (TEX). Loma larga, frente Monterrey, 15 Nov 1966, Jose Luis Gutierrez 220 (TEX). Estación Mariposa between Monterrey and Saltillo, 30 May 1981, M. Lane & M. Leidig 2895 (TEX). Gypsum hills, Santa Rosa, Reyones, n.d., G.B. Hinton 21789 (TEX).

Aphyllon gypsophilum L.T.Collins sp. nov. Type: Mexico: Coahuila: Along road to gypsum dunes 4 miles w of Cuatro Ciénegas hwy [30], 10 Jun 1968, Donald Pinkava 5271 (Holotype: LL, Isotype ASU).

Plants annual, stems slender, 15–21 cm long, 2–3(5) mm diam, unbranched, stem base not enlarged. Roots few simple, mass poorly developed less than 10 mm in diameter. Leaves few, lanceolate, 6–10 mm long, glabrous, margins entire, sometimes minutely ciliate. Inflorescence dense raceme, 3–9 cm long, rarely branched; glandular pubescent, floral bracts 9–10 mm, proximal narrow lanceolate, distal deltoid with apiculate apex, purple tinged, glandular pubescent, apex pubescent. Pedicels 0–3 mm (10 mm proximally), bracteoles 2; Flowers: calyx 7–10 mm, ± symmetric; purple tinged, lobes 4–6 mm, narrowly lanceolate-attenuate; corolla 8–15 (17) mm, tube almost straight, pale, slightly constricted above ovary, glandular pubescent becoming glabrate, lobes purple, 2 mm long, 1–2 mm wide, apex rounded; palatal folds not prominent, pubescent; anthers 1–1.5 mm, glabrous, filament glabrous, pubescent at insertion; Fruit: Capsule oval to ovate, 6–7 mm long. Flowering Apr–Oct. Figure 2.

Diagnosis—Superficially, A. gypsophilum and A. ludovicianum seem almost identical, however, the fine details of the flower and the ecological data clearly separate the two species. Aphyllon gypsophilum can be distinguished from A. ludovicianum by its smaller flowers, extremely short corolla lobes, and deltoid bracts in the inflorescence, and the unique host species Xanthisma gypsophilum (B.L.Turner) D.R.Morgan & R.L.Hartm. and X. restiforme (B.L.Turner) D.R.Morgan & R.L.Hartm. In fact, the host affinity and presence of dimorphic floral bracts sets A. gypsophilum apart from all other species. Aphyllon gypsophilum occurs exclusively in gypsum sand dunes whereas A. ludovicianum is a prairie species primarily parasitizing Artemisia L. spp., Heterotheca spp., and Grindelia squarrosa (Pursh) Dunal.

Distribution and Habitat—Aphyllon gypsophilum appears to be endemic to the Cuatro Ciénegas Bolson which is part the Chihuahuan Desert in the state of Coahuila, Mexico. Within the bolson, the plants only occur in the gypsum sand dunes.

Host—This species parasitizes at least two gypsophilic species of Xanthisma (Machaeranthera). Xanthisma restiforme is endemic to the Cuatro Ciénegas gypsum dunes (Turner 1973). The second host, X. gypsophilum, is another gypsophile widely distributed in the Chihuahuan Desert. This is the first report of a gypsophilic host for the genus Aphyllon and the first report of Xanthisma as host for a species of Aphyllon, though several other species do parasitize its close relative Grindelia.

Etymology—The epithet ‘gypsophilum’ refers to the distinctive gypsum sand dune habitat and the host Xanthisma gypsophilum.

Phylogenetic Affinities—Phylogenetic evidence using nuclear ribosomal genes strongly supports the placement of A. gypsophilum within the A. ludovicianum complex and a sub-clade (BS 5 93) composed in part of the South American taxa A. chilense and A. tacnense (Fig. 3; Schneider et al. 2016). All known hosts parasitized by members of this clade are in the subtribe Machaerantherinae of the Astereae. The single sample of A. gypsophilum resolved sister to the rest of the clade with very weak support (BS 5 66).

Notes—Morphologically, A. gypsophilum resembles A. ludovicianum, but is noticeably smaller in all aspects with slender delicate stems. The flowers are much smaller with rather short narrow corolla lobes (2 mm long by 1 mm wide when dried). The corolla tube is only slightly bent, sometimes essentially straight, and has reduced pubescence, becoming glabrate with age. Inside the corolla tube there is pubescence around the base of the filaments at the insertion, but otherwise the inner tube is glabrous. Although this character occurs in a few other species of Aphyllon, it is not known in Aphyllon ludovicianum which does not have pubescence in the corolla tube. Other taxa known in Mexico also have glabrous filaments.

Most individuals of Aphyllon gypsophilum have two distinctly differently shaped floral bracts (Fig. 2). The lower portion of the inflorescence has lanceolate bracts with acute apices which is typical for the genus. However, in the upper portion of the inflorescence the bracts are oval or deltoid with a distinct apiculate apex (Fig. 2C). These deltoid bracts with apiculate apex have not been reported before in Aphyllon. This is unusual as floral bracts in Aphyllon are generally rather uniform throughout the plant, mostly lanceolate or triangular, varying only slightly in shape, length and width, with an occasional variation of the apex. Hence, they are usually of minimal value taxonomically. This is the first report of dimorphic floral bracts in a species of Aphyllon, though a single specimen was observed with only lanceolate bracts.

Additional Specimens Examined—Mexico. —Coahuila: 1.8 miles sw of Posa de la Becarra opposite Laguna Grande, 9 Jun 1968, Donald Pinkava et al. 5178, (ASU). Along road to gypsum sand dunes 4 miles west of Cuatro Ciénegas hwy, 10 Jul 1968, Donald Pinkava et al. 5276 (ASU). 1.1 mi s of Puerto Salada along road & canal to Santa Tecla, 13 Jun 1968, Donald Pinkava et al. 5564 (ASU). Mt. Anteojo, 17 Jun 1968, Donald Pinkava et al. 5764 (ASU). Tip of Sierra de San Marcos, 10–15 Aug 1968, Janice Lewis s.n. (ASU; Fig. 2B, C). Gypsum dunes 12 mi southwest of Cuatro Ciénegas on Hwy 30, 16 Oct 1971, J. Bacon & W.R. Leverich 1146 (TEX). Gypsum dunes 22 mi southwest of Cuatro Ciénegas, 3 Apr 1972, A.M. Powell & B.L. Turner 2241 (TEX). Gypsum dunes 12 miles southwest of Cuatro Ciénegas, 18 Aug 1973, James Hendrickson 12537 (TEX). Poza El Bonito, Cuatro Ciénegas, Coahuila, 16 Jun 1977, J. Marroquín s.n. (ANSM).