A Brief Review of Literature Taxonomy of Limonium
Limonium is the most species rich and widespread genus of Plum-
baginaceae, although the number of species reported in the genus
is rather speculative. A very high percentage of Limonium diversity
is centered in the Mediterranean basin with nearly 300 taxa current-
ly used in regional floras and checklists [4,5]. A significant portion of
these taxa belong to section Limonium, one of the 12 sections in
which the genus has been traditionally split [6]. In turn, section Li-
monium has been divided into six subsections [6]. Several of these
sections were later grouped into subgeneric ranks. Thus, [7] includ-
ed sections Polyarthrion, Myriolepis, Siphonantha, and Psillyosta-
chys within subgenus Siphonantha. On the other hand, [8] raised
section Pteroclados to the subgeneric level and excluded section
Myriolepis from subgenus Siphonantha to create a new subgenus
(subgenus Myriolepis). Other analytical treatments have dealt with
some of the sections recognized by Boissier and Pax (section Circi-
naria, section Schyzimenium, section Psillyostachis, section
Schyzopethalum, section Pterolimon) as separate genera [9]. Both
sexual (diploid and tetraploid) and apomictic (spanning triploid to
hexaploid cytotypes) species have been reported in section Limoni-
um. Nevertheless, diploid species are few, and polyploid agamic
species constitute the largest portion of the diversity currently
known in this section. Several competing hypotheses, based mainly
on karyological data, regarding the origin of polyploid Limonium
species have been postulated [10]. Suggested that triploid taxa
arose through hybridization between diploid and tetraploid species,
the latter having originated from diploid ancestors [10]. In contrast,
noted that within section Limonium, diploid species show two basic
chromosome numbers (n= 58 and n= 59) and postulated that the
complement of the polyploids arose through several combinations,
involving reduced and unreduced gametes, of the n=58 and n=59
genomes. Hence, triploid (2n= 5, 24, 25, 26, and 27) and tetraploid
(2n 5, 34, 35, and 36) taxa combine genomes of the two basic cyto-
types. Although conflicting, both hypotheses agree that interspecific
hybridization has played a substantial role in the evolution of sec-
tion Limonium. However, this has not been tested by means of a
rigorous phylogenetic analysis. Unfortunately, the very similar mor-
phology exhibited by most members of section Limonium (with most
characters showing continuous variation) has prevented the use of
morphological characters in a phylogenetic (cladistic) context. The-
oretically, molecular analyses could circumvent this drawback and
offer robust hypotheses on the evolution of these species. Molecu-
lar approaches have been applied to some genera with a large
apomictic element in order to detect species (microspecies) bound-
aries and to trace the origins of apomictics [11].
Taxonomic complexity has frequently been related to the mating
system of plants. Hence, taxa having breeding systems favoring
selfing or asexual reproduction (apomixis and clonality) are usually
prone to taxonomical controversy. Apomictic plants circumventing
sexuality, obligately or facultatively, defy classical species concepts
and make the delimitation of taxa a difficult task [12].
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