Taxonomy of an endemic Aristolochia ( Aristolochiaceae ) from the Iberian Peninsula by

Costa, A. 2008. Taxonomy of an endemic Aristolochia (Aristolochiaceae) from the Iberian Peninsula. Anales Jard. Bot. Madrid


Introduction
During a trip in central Spain, in 1986, an interesting new taxon of Aristolochia from the Iberian Peninsula was discovered (Nardi, 1988;Ball & al., 1993).
The overall vegetative appearance, with the exception of a general reduced size of all parts, strikingly resembled A. lutea Desf., a common Central-Eastern Mediterranean species (Ball & al., 1993).A. lutea belongs to the group A. pallida, together with A. pallida Willd., a mainly Central Mediterranean species, and a few endemic species from the Central-Eastern Mediterranean.
All the samples then collected by Nardi seemed to show a globous hypocotyledonary tuberous rootstock, in accordance with the main morphological features of the group; the alternative type, the elongated one, on the contrary, being typical of the A. longa, or A. paucinervis or A. fontanesii, group (Nardi, 1984).All these characteristics (vegetative features, rootstock form and chromosome number) convinced Nardi that the new taxon could be described as A. pallida subsp.castellana Nardi (Nardi, 1988 and pers. comm.), which then became the westernmost of the group and the only one present in the Iberian Peninsula.
During later investigations (Costa, 2002), new collections and observations were carried out on this Iberian taxon, leading to somewhat different conclusions.

Materials and methods
Main diagnostic features measurements of the leaf and flower (Table 1, upper part) were taken from about 20 different herbarium specimens belonging to MA, MACB, MAF and FI (see Appendix).
Special care had been taken when choosing the leaves and the corresponding axillary flower sampled: only completely developed leaves, from the central part of the stem, had been taken into account, avoiding precocious ones (always of reduced size) and also those too young, from the upper part of the stem.
The presence of an inferior, narrow ovary makes difficult the recognition of the peduncle ends.To overcome this problem, we have decided to take into account the sum of the peduncle plus the ovary for the comparisons.
All the new cited measurements of the tuberous rootstock (Table 1, lower part) correspond to living plants from the Alto del Mirlo (Madrid and Ávila, Sierra de Gredos), cultivated in pots for a few years; eventually, these plants unfortunately died.

Taxonomic teatment
From a morphological point of view, the vegetative features of the original description have been confirmed, apart from a general slightly wider range of variation (Table 1, upper part).
Surprisingly, however, the subterranean tuberous rootstock has proven to belong to the elongated type: in young individuals the general shape seems closer to the globous type, but starts elongating in a little older ones (Fig. 1), reaching a notable length in old plants (Table 1, lower part).
All the samples of the holo-and isotypus (Nardi, 1988) are clearly young individuals, which fail to offer a proper representation of the rootstock characteristics.Table 1.Comparison of the main features measurements of the Aristolochia castellana with the protolog (Nardi, 1988).In the lower part are some examples of the size of the tuberous rootstock from samples collected in the Alto del Mirlo (Madrid and Ávila, Sierra de Gredos).In mm; l, length; w, width; bw, width at the base.
In Table 2 the morphological features of A. pallida subsp.castellana are compared with the apparently more related species, such as A. pallida subsp.pallida, A. lutea and A. paucinervis Pomel, the latter always found growing intermixed in the same localities (the data for these other species come from another work in preparation by the author).
As opposed to A. pallida subsp.pallida, A. pallida subsp.castellana shares the chromosome number (2n = 10), like other species belonging to the same group, and some morphological characteristics, such as the leaf shape and the petiole/(peduncle + ovary) ratio.But other features are different: the flower limb is bigger in A. pallida subsp.pallida and the extremely important diagnostic character of the flower limb/tube length ratio is significantly different, being > 1 for A. pallida subsp.pallida, whilst < 1 for A. pallida subsp.castellana.Moreover, the tuberous rootstock shape, as was previously noted, belongs to the elongated type in A. pallida subsp.castellana, whilst belonging to the globous type in A. pallida subsp.pallida.
The overall vegetative appearance of A. pallida subsp.castellana is very similar to that of A. lutea, apart from the generally reduced size of all parts and the petiole/(peduncle + ovary) ratio, which is usually higher in A. pallida subsp.castellana.Moreover, the chromosome number (2n = 8 for A. lutea) and the tuberous rootstock are different, the latter being clearly globous in A. lutea.
The elongated tuberous rootstock type is the same as that of A. paucinervis, which is always found growing intermixed with A. pallida subsp.castellana.But A. paucinervis, which has a very much wider distribution (France, Iberian Peninsula and North Africa) and is probably polyploid (2n = 36; Nardi, 1984), has significantly different vegetative characteristics ( Here below is a proposed modified dichotomous key for the Iberian taxa of the genus Aristolochia (compare with Castroviejo, 1986;Ball & al., 1993):

Distribution and habitat
Similar to other endemic species of the genus in the

a b
Mediterranean region, this taxon distribution is fairly reduced (Fig. 3), this is also probably due to its ecology.
We can usually find it on the wooded slopes of the Sistema Central, usually in fresh and shady localities, preferring slightly acid substrates, which is typical of most of the Mediterranean species of this genus, associated with Quercus spp.(generally Q. pyrenaica), Castanea sativa or rarely Pinus spp., always growing intermixed with Aristolochia paucinervis.
It seems that its presence is correlated with the mountain system and with a mother rock of acid plutonic rock: its presently known distribution, based on herbarium specimens and personal records without voucher (see Appendix), strikingly coincides with the presence of this type of rock in the Sistema Central: Sierra de Gredos westward towards the Valle del Jerte (Cáceres) and a small, isolated area in the Sierra de la Peña de Francia (Salamanca; IGME, 1966;1980).
Although this type of granite is also present in the north of Portugal and Galicia (N-W Spain), to date, no cited locality for this taxon in these areas is known.Of course more investigations would be worthwhile, but it may be that the climatic and ecological conditions are not the most adequate for this taxon.
Also, no locality is yet known in the Sierra de Guadarrama, the eastern part of the Sistema Central, north-east of the Sierra de Gredos, but in this area the mother rock is of a different type (IGME, 1966;1980), which would seem to reinforce the idea of a possible relation between this taxon and the aforementioned geological characteristic, although exactly what type of relation still remains to be studied.

Phylogenetic relationships
The different groups of the Mediterranean species have been defined only on morphological bases (Nardi, 1984).A molecular phylogenetic study could resolve many questions, including the monophyly of the proposed groups.
Nonetheless, the morphological and cytological data described above could already help us to shed light on this subject with regarding A. castellana.
The main morphological feature of the A. pallida group is that of the petiole being very much longer than the peduncle (Nardi, 1984).The most common species of the group, A. lutea and A. pallida, both have a globous tuberous rootstock, whilst the other few, all narrow endemics (Nardi, 1984(Nardi, , 1989)), have an elongated one.The chromosome numbers are 2n = 8; 10, all diploids, with the exception of A. tyrrhena Nardi & Arrigoni (an endemic from Sardinia and Corsica;Nardi & Arrigoni, 1983), with 2n = 26 (Nardi, 1984) and probably polyploid.
Taxonomy of an Iberian Aristolochia Hence, from a morphological and cytological point of view, A. castellana clearly belongs to this group.
The tuberous rootstock shape is worthy of comment.It may depend on some ecological adaptation, depending on the type and humidity of the substrate, the elongated type being more frequent in dry and stony soils and habitats.With regard to this question, the case of A. insularis Nardi & Arrigoni (species belonging to the A. rotunda group; Nardi & Arrigoni, 1983;Nardi, 1984) is extremely interesting.Described at the beginning as a proper species, differing from A. rotunda L. only in its elongated rootstock, it was later changed to a subspecies of the latter, A. rotunda subsp.insularis (Nardi & Arr.) Gamisans (Nardi, 1985;Nardi & Ricceri, 1987), after many intermediate individuals and populations had been found, demonstrating, at least in this case, a sort of variability between the two usually clearly distinguished shapes.
Coming back to A. castellana, we can consider it as the only member of the A. pallida group present in the Iberian Peninsula, the closest species, geographically, of this group being A. pallida, whose westernmost distribution limit is the Rhone Valley in France (Nardi, 1984;Ball & al., 1993).
The A. longa group, whose most common member is A. paucinervis, is mainly morphologically characterized by the elongated rootstock and the short size of petiole and peduncle (Nardi, 1984).The chromosome numbers are 2n = 12; 24; 36 (Nardi, 1984;Nardi & Nesi Nardi, 1987), denoting the presence of polyploidy, even if a proper polyploid series has not yet been demonstrated.
Due to these characteristics, the relation of A. castellana to this group appears unlikely.
All the other taxa of Aristolochia present in the Iberian Peninsula are morphologically, cytologically, geographically and ecologically very distant from A. castellana.
Hybridization seems to be very rare in the genus, with only very few cases known worldwide (Blanco, 2005); no hybrid has yet been described for the Mediterranean species.
We might, therefore, describe A. castellana as a diploid taxon; the westernmost and only one present in the Iberian Peninsula at least distantly related to the A. pallida group species; with a narrow, localized distribution, restricted to a single mountain system, geologically well defined and isolated; spatially close to a polyploid, morphologically different species.
These observations render a recent origin of this taxon for speciation of a present Iberian species very unlikely.

Table 2 .
Comparison of the morphological characteristics of Aristolochia castellana with some apparently related species.The data for A. castellana correspond to 64 leaves from 26 stems; A. pallida 66 leaves / 30 stems; A. lutea 116 / 50; A. paucinervis 81 / 48.In mm; mw, maximum width; the rest of legend as Table1.