Crataegus brachyacantha

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 : 210-212

Comparisons with Crataegus brachyacantha and the Amelanchier clade

Crataegus brachyacantha

Because Crataegus brachyacantha is the Crataegus species branching off closest to Mespilus germanica (e.g., Lo et al. 2007, 2012; Li et al. 2012), it is instructive to compare these two species directly. Crataegus brachyacantha and M. germanica are not particularly similar, beyond characteristics common to the clade. Rather, large differences exist beyond those that distinguish the genera. For example, C. brachyacantha has fruits which are quite small and have a very small hypanthial opening ( Fig. 5 ) and are black (in common with a considerable minority of Crataegus ), has multiflowered, small-flowered inflorescences ( Fig. 6 ) with the typical proleptic Crataegus type A2 inflorescence placement ( Fig. 7 ), sepals much shorter than petals—almost universal in Crataegus , 20 stamens—one of the two common values in Crataegus, and numerous other details. Nevertheless, it does share with Mespilus germanica petals that discolor with age (in M. germanica to pale fawn, in C. brachyacantha to quite a bright orange-yellow, though the phytochemistry of this is unknown), and abaxially hairy, eglandular bracteoles (though these are much smaller and much less hairy in C. brachyacantha ), and very short thorns, mostly characteristics that are rare or uncommon in Crataegus , as well as narrow, unlobed leaves, found in many Crataegus . Thus, Crataegus brachyacantha is, for the most part, already a ‘typical’ Crataegus with substantial morphological divergence from M. germanica . It is therefore evident that at least one of these two, presumably M. germanica , differs greatly from their common ancestor.

The distributions of Crataegus brachyacantha and Mespilus germanica are somewhat similar, though on different continents. Mespilus germanica as a minor fruit is now widely but sparsely naturalized in the southern half of Europe but its native range is from extreme southeast Europe to northern Iran according to Browicz (1968), with northern limits near Yalta, Crimea, at 44° N, and a southern limit at high altitude in Iraqi Kurdistan at ca. 37° N, an area with a predominantly Mediterranean (winter max. precipitation) climatic type. Its greatest wild concentration appears to be across much of northern Turkey and the Caucasus ( Browicz 1968) where the summer precipitation is stronger. The lowest branch on the phylogenetic tree of Crataegus , C. brachyacantha , is known only as a wild plant and occurs in Louisiana, U.S.A. and adjacent states at ca. 29° N – 34° N with an isolated and apparently extinct record in Georgia ( Phipps 1998). This area has a more humid warm temperate climate lacking seasonal precipitation. Both taxa thus occur in regions with mild to moderate winters well to the south of the northern limit of Crataegus , much of the later radiation of which involved adaptation to colder climates.

Time of divergence of Mespilus-Crataegus and similarities to Amelanchier With their considerable differences and somewhat southern locations separated by a large oceanic barrier, the Mespilus-Crataegus divergence must have been long ago, whether it was early Oligocene, e.g., Lo et al. (2012), perhaps via a North Atlantic route, or trans-Beringian in a later warm episode. Since molecular studies by Campbell et al. (2007), Potter et al. (2007), Lo & Donoghue (2012), Li et al. (2012) all unite Mespilus-Crataegus with the Amelanchier clade it is likely that their common origin is in the New World as believed by Lo et al. (2009). Lo et al. (2009) left the location of common origin ambiguous but considered it to result in a North Atlantic vicariance. If so, the Mespilus ancestor, as an early disperser to the Old World, has apparently left only one extant descendent there, M. germanica . The deep relationship to the Amelanchier clade is supported by Mespilus bracteoles (very large, eglandular, abaxially hairy) being similar to those of many Amelanchier species and by both these genera having two locations of origin of the annual reproductive shoot (lateral to extension shoots and at the tips of woody short shoots), as noted above.

Inflorescence type and position

The Maloid inflorescence is of a monopodial and monotelic construction, usually branched to at least the second order, with 1 to several hundred flowers. Anthesis is normally in spring and the inflorescence is usually terminal on a relatively few-leaved fertile shoot of the season, the uppermost leaf or two of which are sometimes bracteal. Mespilus differs from Crataegus by having 1 to few flowers per inflorescence vs. 1 to ca. 50.

The location of origin of the flowering shoot varies in the Crataegus and Amelanchier clades. The origin may often be subterminal on a woody shoot, itself commonly a short shoot. I will provisionally call this fertile shoot position (i.e., terminal or subterminal on woody short shoots) ‘ type A’. However, it is interesting to note that the flowering shoot may instead be borne lateral to the extension shoot, which position I will provisionally call ‘ type B’. The type A situation is seen in Amelanchier arborea (Michaux f.) Fernald ( Fig. 8c ) and also in all the inflorescences in A. laevis Wiegand ( Fig. 9 ) while the type B situation may be clearly seen in the same specimen of A. arborea ( Fig. 8b ). Similarly, in wild-sourced Mespilus germanica specimens cultivated at Copenhagen and Kew, both type A ( Fig. 10 ) and type B ( Fig. 11) fertile shoot origins may be observed. With regard to Crataegus , by far the predominant situation is type A, with the leafy flowering shoot arising subterminally from a woody short shoot, as illustrated in C. brachyacantha ( Fig. 7 ). In Crataegus , the type B origin was first noticed by Phipps et al. (2006) in the widespread though only locally occurring southeast United States species C. triflora Chapman of C. ser. Triflorae ( Fig. 12 ). It is believed that this was the first explicit record of the different origins of the fertile short shoot in Maleae . The type B situation has since been recognized in the apparently extinct C. austromontana Beadle of the same series, and to a limited extent in C. harbisonii Beadle of the related C. ser. Bracteatae ( Phipps et al. 2006), perhaps itself a hybrid of C. ser. Triflorae. It can also occur in the Chinese species C. cuneata and may also occasionally be seen in C. uniflora (C. ser. Parvifoliae ), the only Crataegus , like M. germanica , with sepals longer than petals. Thus, neither inflorescence type nor position of origin of the fertile shoot separates Mespilus from Crataegus . On the other hand, inflorescences arising from woody short shoots (type A) in Amelanchier may be separated from those of Mespilus and Crataegus by being borne on terminal (type A1) or subterminal (type A2) buds in Amelanchier and from subterminal buds only in Mespilus and Crataegus (type A2).

Lo et al. (2007) correctly pointed out that the Amelanchier and Crataegus clades differ by much more than do the sister genera Mespilus and Crataegus . In emphasizing this fairly deep separation they draw attention to the presence of sylleptic growth of vegetative shoots from the fertile shoots of Amelanchier (see a, Fig. 8 ), a feature not observed in the Crataegus clade, nor indeed, in most of the Maleae . However, the situation appears to be more complicated than this as sylleptic branching has so far not been detected in Peraphyllum or Malacomeles , the other two members of the Amelanchier clade and thus that clade cannot be defined by this. In fact, it is worth asking whether sylleptic growth in Amelanchier is not merely reflective of the elongated, racemose inflorescence form common in Amelanchier , and apparently unique in Maleae , which allows space for such sylleptic growth to take place. Indeed, even though it is quite common in the genus, sylleptic branching from reproductive shoots in Amelanchier clearly does not occur below all inflorescences. Likewise, the corollary which Lo et al. (2007) note, a proleptic fertile shoot arising from a subterminal dormant bud, generating a sympodial short shoot system, does not appear to be universal in Mespilus-Crataegus, though it is by far the most common.

With regard to the Malacomeles and Peraphyllum subclade of the Amelanchier clade, perennial short shoots, if any, are extremely short and in Malacomeles nervosa (Decaisne) G.N. Jones , the fertile shoot bearing an inflorescence may on occasion arise from a leaf axil as is evident in Phipps 5889 (UWO!) from Comitán, Chiapas, Mexico, collected in October (1985). Neither do Malacomeles and Peraphyllum show any sign of sylleptic branching from the leafy part of the shoot below the inflorescence as mentioned above. It thus seems that use of the feature of sylleptic vs. proleptic branching to separate the two subclades does not work.

The complicated issues of inflorescence position and sylleptic branching in the inflorescence aside, Lo et al. (2007) detail many differences between the Amelanchier and Crataegus subclades. I regard the most powerful of these as the carpellary differences in flower, and the hard elements in fruit. In the Amelanchier subclade the seed is the hard part that is not digested by the frugivore and which is excreted; in the Mespilus-Crataegus subclade, it is the carpellary wall that is hardened. Thus two very different fruit types are created—a pseudoberry and a pyrenous pome.

Figures

FIGURE 5. Crataegus brachyacantha infructescence showing blackish fruit with small hypanthial opening. Texas. (photo R.W. Lance).

FIGURE 6. Crataegus brachyacantha inflorescences showing numerous small flowers on type A inflorescence. Texas.

FIGURE 7. Crataegus brachyacantha. Note short shoot bearing fruit. Louisiana.

FIGURE 8. Amelanchier arborea. Herbarium specimen in flower. Note sylleptic growth (at a), and types A and B inflorescence origin, arrowed (respectively at c2 and b). Ontario.

FIGURE 9. Amelanchier laevis. Flowering herbarium specimen. Note type A1 inflorescence origin, with short shoots, arrowed. Ontario.

FIGURE 10. Mespilus germanica. Fruiting herbarium specimen; wild type. Note type B origin infructescences, arrowed. Cult., Kew.

FIGURE 12. Crataegus triflora flower. Note large stamen no. (ca. 35), first report of this (photo 12.iv.1999), flower diam. ca. 27 mm. Alabama.