Crataegus

Phipps, James B., 2016, Studies In Mespilus, Crataegus, And × Crataemespilus (Rosaceae), I. Differentiation Of Mespilus And Crataegus, Expansion Of × Crataemespilus, With Supplementary Observations On Differences Between The Crataegus And, Phytotaxa 257 (3), pp. 201-229 : 215-224

Crataegus L. (1753: 475).

Type: Crataegus oxyacantha L., nom. rejic. (= C. rhipidophylla Gandoger ).

Shrubs or small trees, 0.5–8 (–12) m. Bark of trunk commonly grayish or gray-brown, when older flaking and revealing orange-brown fresh bark, alternatively deeply corrugated and dark, more rarely smooth and finely exfoliating or smooth and with horizontal lenticels; on younger stems (1–2 cm diam.) usually pale to dark gray, seldom with horizontal lenticels. Twigs usually armed with straight to curved, dark when young, determinate thorns, 1–6 (–11) cm, or rarely +/- unarmed; else twigs tipped with indeterminate thorns; woody short shoots present; current growth glabrous to tomentose. Winter buds 2–4 mm, usually spherical, sometimes subconical, 6–10-scaled, scales imbricate, usually dark shiny reddish. Leaves simple, entire to deeply pinnatifid margins usually with numerous small, even teeth, 1–8 (–10) cm, suborbiculate to narrow-lanceolate, widest part variably positioned, glabrous to variably pubescent, 1–10- veined per side, venation commonly craspedodromous, sometimes camptodromous. Inflorescences 1–50-flowered shallowly domed monopodial panicles (or in few-flowered forms reduced to racemes or uniflory), with about 2–8 leaves below the flower(s), sometimes with leafy bracts subtending proximal branches; usually subterminal on short shoots (type A 2) or borne terminally or laterally direct on extension shoots (type B); bracteoles few to numerous 2–15 mm long, linear to narrow-ovate, usually acute, +/- membranous to subherbaceous, caducous to persistent, abaxially hairy or glabrous, commonly gland-margined. Flowers: 8–25 mm diam., perigynous; hypanthium +/- obconic, constricted around disc, disc saucer-shaped except for style opening; sepals 5, free, distinct, triangular, usually much shorter than petals, margins entire to serrate or sometimes laciniate, the teeth gland-tipped; petals 5, 3–12 mm, free, white (except pink to red in mutants), usually suborbiculate, barely clawed, +/- entire margined; stamens 5-ca. 20 (usually ca. 10 or ca. 20, in Crataegus triflora 30–45), anthers white to cream or anthocyanic (pink to red or purplish); carpels 1–5, free but laterally touching, adnate to hypanthium, styles 1–5, lateral and adnate to ventral side of carpel for most of length, free, exserted from hypanthial opening, ovules 2, superposed. Pomes: subspheric to ellipsoid or pyriform, 6–15 (–20) mm diam. (– 25 mm or somewhat larger in some cultivars), red to yellow or purplish to black at maturity, glabrous to tomentose, sometimes punctate; flesh often becoming soft, often insipid, sometimes sweet and pleasant to eat; hypanthial opening present (tissues of disc absent), 10–35% width of fruit; sepals often persistent, sometimes erose or circumscissile, appressed to erect, bases usually nearly touching; shriveled filaments and dried styles often persisting though may be erose; pyrenes 1–5, within hypanthial enclosure though tips sometimes visible, very hard, dorsally grooved, sides smooth or pitted. x = 17 (2n = 34, 51, 68, usually).

Ca. 250 species, north temperate regions; a few introduced in southern hemisphere temperate regions and tropical

Andes.

Review of × Crataemespilus

× Crataemespilus Camus (1899: 326) . ( Figs. 4 , 13–16 , 19–24 )

Type: Crataemespilus × grandiflora (Smith) E.G. Camus (= Mespilus grandiflora Smith ).

It is difficult to characterize nothogenera and no real attempt will be made to do so. Suffice it to say that all three nothospecies have obvious similarities to Mespilus germanica and two also show similarities to particular Crataegus species. Figure 13 illustrates a collage of the European taxa taken from Beck in Reichenbach (1914).

× Crataemespilus was erected by E.G. Camus in 1899 to accommodate a presumed intergeneric hybrid originating in European horticulture that had first been described as a Mespilus , even though it was already firmly believed to be an intergeneric hybrid. Byatt et al. (1977) concurred with Smith’s ‘very unambiguous statement concerning the parentage’ that C. laevigata (Poir.) DC. was one parent, particularly on the basis of leaf shape. In 1914 Beck added to × Crataemespilus the very rare, naturally occurring, presumed nothospecies C. × gillotii , proposing the parentage C. monogyna × M. germanica , this interpretation being accepted by Byatt et al. (1977) as reasonable. Gillot (1876) had already published the latter nothotaxon under the invalid name C. oxyacantha-germanica and held it to have the same origin. We may now recognize three nothospecies in × Crataemespilus , the third, added in this paper, being based on Mespilus canescens . For those who wish, the three nothospecies of × Crataemespilus may be placed in two nothosections, as set out in Lo et al. (2007), and the authors of Crataegus nothosect. × Phippsara T.A. Dickinson & E.Y.Y. Lo are thanked for their generous comments.

Attempts to substitute the prior name + Crataegomespilus Simon-Louis ex Bellair (1899: 482) should be rebuffed. Not only is the name invalid under the Code, but this strange organism is an unstable chimaera produced by grafting, in which tissues of the Crataegus and Mespilus are intermixed, giving at first an appearance of hybridity. As plants of this so-called ‘graft-hybrid’ age there tends to develop a segregation of tissue such that pure branches of Mespilus or Crataegus may be seen. Older bushes sometimes revert fully, at least as far as macroscopic observation is concerned, to either Mespilus or Crataegus . In my view, such plants (there are few other examples), in which the two genomes are haphazardly and unstably arranged cannot be equated with normal taxa.

Crataemespilus × grandiflora is well known in cultivation and its variability apparently encompasses the narrow range of the variability of C. gillottii . Consequently, these two European hybrids cannot at this stage be convincingly separated in a key although the characters used by Beck will be used in an attempt to do so. Note that the very low level of sexual fertility of all three nothospecies of × Crataemespilus underscores the width of these hybrids and further supports the recognition of Mespilus as distinct from Crataegus in line with the earlier general discussion of intergeneric hybrids in the Maloideae .

Key to nothospecies of × Crataemespilus yellow; fruit 8–12 mm, bright red; Arkansas, USA................................................................................................ 3. C. × canescens

- Bushes with 1 to several stems, latter divergent; leaves shiny green at maturity; inflorescences uniflorous to 2–4-flowered, cymosepaniculate; petals entire or sometimes slightly notched; anthers pink; fruit 12–15 mm, golden ripening to burgundy; western Europe .............................................................................................................................................................................................. 2.

2. Stipules entire; leaves completely lacking lobes or sometimes with slight bulges .............................................. 1. C. × grandiflora

- Stipules serrate; some leaves distinctly lobed ............................................................................................................... 2. C. × gillotii

1. Crataemespilus × grandiflora (Smith) Camus (1899: 326) . Mespilus grandiflora Smith (1805: 33) . Mespilus smithii Candolle (1825: 633) , nom. illeg. superfl. Crataegus smithii Chalon (1868: 174) , nom. inval. ( Figs. 13 (4–9), 14–16)

= Mespilus lobata Poiret (1816: 71) . Crataegus lobata (Poiret) Bosc (1821: 223) .

Bush or small tree, 2–5 m; trunks 1 to few. Reproductive short shoots present; twigs sometimes with a few short thorns, young growth pubescent. Leaves 3–6 cm, commonly broad elliptic, sometime obovate, then shallowly 1-lobed per side, lobes rounded to subacute, margins +/- serrate, glabrous, or pubescent abaxially, venation semi-camptodromous, midvein pubescent adaxially and abaxially. Inflorescences subterminal from short shoots (type A2; Fig. 15 ), 1–3 (–5)- flowered; bracteoles few, 3–12 mm, narrow-ovate (shorter) to linear (longer), scarious, fawn, caducous, glabrous, eglandular. Flowers (flat) 22 mm diam. in K.R. Robertson 3519 (UWO!) and 30 mm diam. in KRR 3319 (UWO!); hypanthium dense-pubescent, disc dense-villous centrally, peripherally glabrous; sepals triangular, ca. 35% petal length, margins glandular serrate; petals cupped, sometimes slightly notched, white (pale fawn when dried); stamens ca. 23–25, anthers pink; styles 2–3. Fruit +/- spheric, ca. 12–15 mm, glabrous, golden ripening to burgundy; hypanthial opening wide (ca. 50%); sepals very narrow, margins entire, +/- erect to wide-spreading; pyrenes 2–3, tips exposed.

Crataemespilus × grandiflora is regarded by Byatt et al. (1977), primarily on the basis of Smith’s (1805) unequivocal statement, as having the origin Crataegus laevigata Poir. × Mespilus germanica L. It is intermediate between its two parents. There are no certain wild records but it is quite widely cultivated as an ornamental, for which purpose it is excellent. Mature small trees of this nothospecies line suburban roads such as in Harborne, Birmingham, UK, for instance. It may be found in many of the more prominent arboreta and is also offered for sale commercially on a small scale. Plants are normally propagated by grafting rather than attempting to recreate the plant by controlled pollination.

Plants of Crataemespilus × grandiflora are seed sterile and pollen was ca. 4.5% sound ( Byatt et al. 1977).

2. Crataemespilus × gillotii Beck (1914: 30 , t. 107). Crataegus gillotii (Beck) T.A. Dickinson & E.Y.Y. Lo in Lo et al. (2007: 609). Crataegus oxyacantha-germanica Gillot (1876: 14–25) , nom. inval. ( Fig. 13 , 1–3 )

Description as Crataemespilus ×grandiflora except for key characters. In the small sample involved the leaves range from entire-margined (relatively few) to deeply lobed, the stipules are serrate, and the styles 2, as may be seen in Fig. 13 (1–3) taken from Beck (1914).

Crataemespilus × gillotii is intermediate between Mespilus germanica and Crataegus monogyna and the differences from Crataemespilus × grandiflora are few. This nothotaxon rests on material from its type location, Autun, Saône-et Loire, France, where it was found in a hedge. It is seldom, if ever, cultivated.

Crataemespilus × gillotii was first recognized by Gillot (1876) under the name Crataegus oxyacantha-germanica . Gillot’s lengthy and detailed paper carefully distinguishes the hybrid from its parents and although he called one parent C. oxyacantha he recognized two elements within it— C. monogyna and ‘ C. digyna ’ (now C. laevigata (Poir.) DC. )—and pointed out that the depth of leaf lobing of the hybrid suggested C. monogyna was the actual parent. Beck (1914) later honoured Gillot in his specific epithet. Byatt et al. (1977) confirmed the parentage M. germanica × C. monogyna .

3. Crataemespilus × canescens (J.B Phipps) J.B. Phipps , comb. nov. Mespilus canescens Phipps (1990: 26–32) . Crataegus canescens (J.B. Phipps) T.A. Dickinson & E.Y.Y. Lo in Lo et al. (2007: 609). ( Figs. 4 , 19–24 )

Holotype: U.S.A. Arkansas: Prairie Co., 2 mi S of Slovak , 15 Apr. 1970, J. E. Stern s.n. ( UARK!).

Stern’s Medlar.

Bush, 2–5 m, stems slender, fasciculate; bark exfoliating in irregular strips, various pale colors. Reproductive short shoots sometimes present; twigs sometimes with a few straight thorns 2–4 cm, young growth canescent. Leaves 2–4 cm, narrowly elliptic to narrowly obovate, margins finely serrate distally, entire proximally, venation camptodromous, veins 5–7 per side, canescent. Inflorescences racemes (larger sub-paniculate) borne either terminating woody short shoots (type A), or lateral to and terminal on extension shoots (type B), 2–6-flowered; bracteoles several, 5–15 mm, very narrow, acuminate, margins sometimes with very narrow, long teeth, firm, green, persistent, hairy, with several very large, ellipsoid marginal glands. Flowers 18–20 mm; hypanthium canescent; disc saucer-shaped, bristly around style bases; sepals triangular, 25–30% petal length, margins entire, abaxially canescent; petals cupped, notched, white (fawn when dried); stamens ca. 20, anthers pale yellow; styles 5. Fruit +/- spheric, 8–12 mm, glabrescent, usually with residual indumentum least at ends, bright to deep red; hypanthial opening ca. 30–50% width of fruit; hairy residual disc tissue sometimes present; sepal remnants usually present; pyrenes 5, tips usually exposed.

The small red fruit is hawthorn-like and usually solitary ( Fig. 24 ). It produces pyrenes but few seeds. Stern’s Medlar has excellent ornamental characteristics as summarized in Phipps (1990) and Phipps et al. (2003) and is already produced commercially on a small scale for ornamental horticulture. Lo et al. (2007) showed that Crataemespilus × canescens was a hybrid of Mespilus germanica (cultivated or escaped) and C. brachyacantha (wild), presumably originating at or close to where it is found today in Arkansas. Intriguingly, they also averred that there was an additional, red-fruited, Crataegus ancestor for × C. canescens but did not suggest what it might be, a matter that will be discussed in a future paper.

Figures

FIGURE 1. Mespilus germanica. Fruiting branches of wild type. Note fruit about 15 mm diam. with wide hypanthial openings. Cult., Kew. (photo K.R. Robertson).

FIGURE 2. Mespilus germanica. Wild type in flower, diam. ca. 30 mm. Note some petals notched, long sepals, 28–30 stamens, red anthers. Cult., Kew.

FIGURE 3. Mespilus germanica. Fruit of cv. Nottingham. Note proportionately broad leaves, very large fruit (ca. 35 mm diam.), widespaced, very long sepals. Arrowed are: (a) style projecting through disc tissue; (b) undulating surface of disc tissue covering pyrenes; (c) split in side of fruit caused by inadequate allometric growth. Cult., Ailsa Craig, Ontario.

FIGURE 4. Crataemespilus ×canescens flowers. Note large size (ca. 25 mm diam.), ca. 20 stamens, yellow anthers, notched petals. Arkansas.

FIGURE 13. ×Crataemespilus collage. Crataemespilus ×gillotii 1–3 (lhs); C. ×grandiflora 4–9 (rhs). Note deeper leaf lobing in C. ×gillotii, deeper stipule lobing in C. ×grandiflora (from Beck 1914).

FIGURE 14. Crataemespilus ×grandiflora trunk showing exfoliating bark; freshly exposed bark bright orange-brown. Cult., Kew. (photo K.R. Robertson).

FIGURE 15. Crataemespilus ×grandiflora flowering herbarium specimen. Note short shoots, arrowed. Cult., Kew.

FIGURE 16. Crataemespilus ×grandiflora immature fruits. Note leaves proportionately broader than wild-type Mespilus germanica, smaller hypanthial openings, fr. diam. ca. 15 mm. Cult.. Kew. (photo K.R. Robertson).

FIGURE 19. Crataemespilus ×canescens habit. Note fasciculate trunks. AR.

FIGURE 20. Crataemespilus ×canescens trunk showing loosely exfoliating bark; freshly exposed olive-green. Arkansas.

FIGURE 21. Crataemespilus ×canescens inflorescence in bud. Note leafy bracts; long, narrow, green, herbaceous bracteoles, arrowed. Arkansas.

FIGURE 22. Crataemespilus ×canescens inflorescences. Note pendulous axis, upcurving of pedicels. Arkansas.

FIGURE 23. Crataemespilus ×canescens flowering herbarium specimen; a = leafy bract; b = bracteole; c = main axis; d = example of type B inflorescence origin.

FIGURE 24. Crataemespilus ×canescens fruit. Note relatively small size (ca. 10 mm diam.), red color. Arkansas.