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Title: Outline analysis for identifying Limodorum species from seeds
Authors: Magrini, Sara
Buono, Sergio
Gransinigh, Emanuele
Rempicci, Massimiliano
Onofri, Silvano
Scoppola, anna
Keywords: image analysisorchidsidentificationplants
Issue Date: 2010
Publisher: EUT Edizioni Università di Trieste
Source: Sara Magrini [et al.], Outline analysis for identifying Limodorum species from seeds, in Pier Luigi Nimis and Régine Vignes Lebbe (eds.): “Tools for Identifying Biodiversity: Progress and Problems. Proceedings of the International Congress, Paris, September 20-22, 2010”, Trieste, EUT Edizioni Università di Trieste, 2010, pp. 249-250.
Limodorum trabutianum Batt. is an orchid species of the
Italian flora, with a central-western stenomediterranean distribution,
that is sporadic in the western part of the distribution area of the more
common L. abortivum (L.) Sw., an eurimediterranean species. It occurs
in Italy only with a few populations in Tuscany, Latium, Umbria, Sicily
and Sardinia [1], often with L. abortivum [2], [3], [4] from which it is
easily recognizable only during anthesis for the denser inflorescence
spike, the ribbon-like lip without differentiation in epychile and
hypochile, and for the spur that is very short or absent [5]. On the
contrary, the identification of these two taxa during the fruiting phase
is rather difficult or even impossible. The aim of this study is to verify
the taxonomic value of Limodorum seeds, particularly of their shape,
as highlighted from recent studies for other orchids [6], [7], in order to
establish its usefulness for recognizing the two species.
We have identified 5 Italian populations of the two taxa: 2 populations
of L. trabutianum, one within the Marturanum Regional Park
(Barbarano Romano, Viterbo), the other near Cortona (Arezzo), and
3 populations of L. abortivum, near S. Martino al Cimino (Viterbo),
in the M. Casoli Reserve (Bomarzo, Viterbo), and in the same site
of L. trabutianum within the Marturanum Park. The phenology of
these populations was monitored to collect mature seeds from
naturally dehiscing capsules. The intra- and interspecific variability of
seed shapes was analyzed with the methodology of Elliptic Fourier
descriptors [8], which allows to describe in terms of harmonics each
two-dimensional shape with a closed outline. For this outline analysis
we used the software package SHAPE 1.3 [9]. An average of 100
seeds from each species and from each site was photographed with
a NIKON Coolpix 5000 camera mounted on a LEITZ-ARISTOPLAN
microscope, obtaining 500 digital images with a resolution of 300
dpi and a size of 800 x 1000 pixels. All images were prepared using
Adobe Photoshop 7.0: as a first step, every foreign element was
eliminated from the picture, thereby isolating the single seed, then its
contrast with the background was maximized, and finally all images
were saved in .bps format (24bit). The color images were converted to binary with Chain Coder before tracing the outlines in Chain-code,
a coding system that describes the geometrical information of the
shapes. Then the Chain-code file was transformed into a Normalized
Elliptic Fourier file using Chc2Nef using 20 harmonics. The matrix of
the harmonic coefficients underwent a process of data normalization
based on the first harmonic, to transform the data into shape
variables. Subsequently, a PCA was performed on the variancecovariance
matrix of normalized coefficients using PrinComp, which
gives a graphical output of the principal components (average shape
± standard deviations).
The first results of the outline analysis confirm a low intraspecific
variability of seed shape, but show a very high interspecific variability:
L. abortivum seeds are very elongated, from fusiform to filiform, while
L. trabutianum seeds are much wider and have a very lower length/
width ratio. These results allow to distinguish between these two
species even during the fruiting phase, simply using seed shape as
a diagnostic character, avoiding the use of traditional morphometric
analysis which need microscopic measurements.
Type: Book Chapter
ISBN: 978-88-8303-295-0
Appears in Collections:Tools for Identifying Biodiversity: Progress and Problems

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