Xochiquetzallia (Asparagaceae, Brodiaeoideae), a new genus segregated from the paraphyletic Dandya

Abstract A new genus, Xochiquetzallia, for the Brodiaeoideae, Asparagaceae family is here proposed. A taxonomic analysis based on morphology highlights its synapomorphies. The characters that distinguish Xochiquetzallia are the absence of a pith in the gynophore and the presence of an entire stigma. The recognition of Dandya purpusii as a monotypic genus is supported by the development of a short floral tube (< 2 mm) and a pith in the gynophore, as well as a divided stigma shared with the other genera of the Milla clade, Bessera, Jaimehintonia, Petronymphe and Milla. A key to its taxonomic determination is given for both the Xochiquetzallia species and the Milla clade genera.


Introduction
Dandya H.E. Moore is a genus endemic to Mexico and one of the five genera of the Milla clade (Gutiérrez et al. 2017). Dandya purpusii (Brandegee) H.E. Moore, the type species, has been placed in several genera in the past (Moore 1953) and molecular evidence suggest that generic limits in the complex are weak when few species are included in their phylogenetic analyses (Pires et al. 2001, Pires and Sytsma 2002, Gándara et al. 2014. Recently, Gutiérrez et al. (2017) conducted a study on the phylogeny of the Milla clade based on morphological, anatomical and molecular evidence (cDNA and ITS) and recovered two clades (Fig. 1). One clade recovers three species of Dandya plus Milla mortoniana strongly supported as sister to Dandya purpusii and the other four genera of the Milla clade (Bessera, Jaimehintonia, Milla and Petronymphe). Their results showed apomorphic structural characters that support the genera. The analyses clarify the phylogenetic relationships of genera and species of the Milla clade. The most relevant outcome is that Dandya is paraphyletic where three species of Dandya with distribution in the Balsas River Basin share the same ancestor as Milla mortoniana (Fig.  1). These four species (D. balsensis, D. hannibalii, D. thadhowardii and M. mortoniana) have as a synapomorphy the entire stigma. The genus Milla is paraphyletic due to the exclusion of Milla mortoniana. The members of Milla share four synapomorphies (thin pedicel, floral tubes > 60 mm, anthers with a bicollateral bundle and 20-30% of the ovary adnate to the floral tube) not present in M. mortoniana. Dandya purpusii shares with Bessera, Jaimehintonia, Milla and Petronymphe the dissected stigma, but no other character is mentioned. Based on Gutiérrez et al. (2017) results, here we identify characters that are consistent with the phylogeny and create a new genus for the clade of Dandya and a Milla species, Dandya is circumscribed, and taxonomic keys are given that allow differentiating the genera of the Milla clade and the new genus.

Material and methods
Plant morphology was analyzed from field collected and herbarium material (ARIZ, BH, CHAPA, F, FC, GH, IEB, JEPS, MEXU, NY, RSA, UAMIZ, US and XAL). We studied the floral morphology from organisms collected in the field, except for Milla mortoniana (material removed from herbarium, MEXU). Morphological characters, vegetative and reproductive, were observed and analyzed with the help of a microscope (Nikon SMZ-2T) and terminology follows various authors (Moore 1953, Lenz 1971, Rahn 1998, Harris and Harris 2001. In addition, floral and foliar anatomical characters (Gutiérrez et al. 2010(Gutiérrez et al. , 2015 were incorporated. The complete list of 60 characters and characters' states used to delimit the monophyletic groups for the Milla complex can be consulted in Gutiérrez et al. (2017). Those characters that were recovered as synapomorphies or unique character combinations are here used to construct the keys for the Milla complex genera and the species of the new genus here proposed.

Results
Based on the phylogenetic clades recovered by Gutiérrez et al. (2017) and the deep morphological analysis of the species, we proposed the amended circumscription of Dandya and the new genus Xochiquetzallia.
Etymology. This genus is named in honor of the goddess of Aztec flowers, in Nahuatl "Xōchiquetzalli" (beautiful flower) "xṓchitl" (flower), "quétzalli" (beautiful). The Aztecs developed majestic architectural works, had extensive knowledge of astronomy and great respect for nature, particularly plants.
Key to the taxonomic determination of the genera of the Milla clade
López-Ferrari and Espejo-Serna (1992) pointed out that Xochiquetzallia balsensis differs from X. thadhowardii by the size of the perigonium, filament and style segments, smaller in X. balsensis. Also, these authors indicate that in X. thadhowardii the anthers are firmly united among them around the style whereas in X. balsensis they are free. No differences in the morphological and anatomical characters were found between both species  (Gutiérrez 2009;Gutiérrez et al. 2010Gutiérrez et al. , 2015. The analysis carried out by Gutiérrez et al. (2017) shows that the population of the here proposed Xochiquetzallia balsensis from the state of Morelos is the only one that differentiates itself by the size of the filaments and the style as proposed by López-Ferrari and Espejo-Serna (1992). Based on our field observations in the type locality of Xochiquetzallia balsensis we confirm that their anthers are firmly united among them around the style as in X. thadhowardii and the separation of the anthers takes place in advanced stages of the anthesis, as occurs with X. thadhowardii. In this sense, it is concluded that Xochiquetzallia balsensis should be circumscribed by its filaments no larger than 3 mm long and less than or equal to 4 mm long.

Discussion
In Dandya and Xochiquetzallia, the connate stamens have been a recurrent character in the descriptions (Moore 1953;Lenz 1971;López-Ferrari and Espejo-Serna 1992). The staminal connation has been described as "crown or cup" at the base of the stamens and it was considered a diagnostic character for Dandya. Gutiérrez et al. (2010) did not find connate stamens in Dandya and Xochiquetzallia in their floral development study of the Milla complex. Moreover, they discovered that what was called "crown or cup" is the base of the filaments that is wider than the upper part and gives the appearance of detaching when the stamens are released asynchronously. Gutiérrez et al. (2010), also showed that Bessera is the only genus of the Milla clade that has connate filaments.
The existence of gynophore has also been a controversial feature. A gynophore was not described for the former species of Dandya now in Xochiquetzallia (X. balsensis, X. hannibalii and X. thadhowardii ;Lenz 1971;López-Ferrari and Espejo-Serna 1992). Gutiérrez et al. (2010), when studying the gynophore, checked if it exists in the Xochiquetzallia species. They found that, unlike other genera of the Milla clade, the gynophore is short (< 2 mm) and lacks a pith. Also, Xochiquetzallia balsensis, X. hannibalii and X. thadhowardii have an entire stigma, a character shared with X. mortoniana which also lacks a pith in the gynophore. A recent study of floral anatomy of Dandya purpusii, allowed us to confirm that this species does have a pith in the gynophore as also found in Bessera, Jaimehintonia, Milla and Petronymphe (Gutiérrez et al. 2017). The short floral tube (< 2 mm) of Dandya purpusii was previously used as evidence to classify this species with the species of Xochiquetzallia (Dandya) (X. balsensis, X. hannibalii and X. thadhowardii) (Lenz 1971;López-Ferrari and Espejo-Serna 1992). However, the presence of the pith and the dissected stigma were not considered, and now we know both characters present in Dandya purpusii are shared with the other four genera. Dandya purpusii is distinguished by its ephemeral flowering and has been scarcely collected after its description in 1911 (Brandegee 1911). Further explorations in the distribution area of Dandya purpusii, now recognized as the only species of the genus Dandya, will hopefully reveal more localities and potentially the discovery of other species that are difficult to locate due to their ephemeral reproductive biology. The disjunct distribution between Dandya purpusii and the species of Xochiquetzallia suggests that both genera evolved independently and converged on floral shape as an adaptation to pollinators, among them the Lepidoptera. Moore (1953) considered the floral shape as a discrete character that allowed to separate the genera of the Milla complex; for example, diagnostic floral shapes include subcampanulate for Dandya, tubular in Petronymphe, tubular and campanulate in Bessera, and hypocrateriform in Jaimehintonia and Milla. Xochiquetzallia mortoniana presents hypocrateriform flowers and this character allowed Moore (1953) to classify this species as Milla. Our investigations here found that Bessera species have all floral shape variations described in the genera of the clade (Bessera tuitensis has subcampanulate flowers, B. elegans campanulate, and B. tenuiflora tubular). The floral shapes among Xochiquetzallia species are either hypocrateriform or subcampanulate.