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. 2017 May 31:5:e3399.
doi: 10.7717/peerj.3399. eCollection 2017.

Seed morphometric characteristics of European species of Elatine (Elatinaceae)

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Seed morphometric characteristics of European species of Elatine (Elatinaceae)

Agnieszka Popiela et al. PeerJ. .

Abstract

Elatine L. contains ca. 25 small, herbaceous, annual species distributed in ephemeral waters in both hemispheres. All species are amphibious and characterized by a high degree of morphological variability. The importance of seed morphology in Elatine taxonomy has been emphasized by many authors. The degree of seed curvature and seed coat reticulation have been traditionally considered very important in recognizing individual species of this genus. Seed morphometric characteristics of 10 Elatine species, including all European native taxa, are provided on the basis of material from two or three populations of each species. A total of 24-50 seeds were studied from each population, altogether 1,260 images were used for the morphometric study. In total, six parameters were measured from SEM pictures: object surface area, profile specific perimeter (object circuit), rectangle of the object (a) length, rectangle of the object (b) width, angle of the seed curvature, and number of pits in the seed coat counted in the middle row. Our study shows that the range of morphological variation of seeds in European species of Elatine is great, both between the species and the populations. Discrimination analysis showed that all six traits significantly differentiate the populations studied (λ = 0.001, p < 0.001), and the greatest contributions were "number of pits", "rectangle_a", and "the angle curvature". Multidimensional scaling based on a correlation matrix of Mahalanobis distance of the six features studied revealed the greatest similarity between the three populations of E. alsinastrum, E. macropoda, and E. hexandra. Regarding interspecific differences, a Kruskal-Wallis tests showed that, in many cases, lack of statistically significant differences between species relative to the studied seed traits. If distinction of species is only based on seeds, especially if only a few seeds are evaluated, the following species pairs can be easily confused: E. alsinastrum and E. orthosperma, E. hexandra and E. macropoda, E. campylosperma and E. hydropiper, as well and E. gussonei and E. hungarica. We found no diversity in seed coat micromorphology within pits that could have potential taxonomic importance. An identification key and descriptions of species are provided on the basis of seeds traits.

Keywords: Amphibious species; Determination key; Ephemerals; Malphigiales; Micromorphology; Morphology; Population; SEM; Seed coat; Seeds traits.

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Conflict of interest statement

The authors declare there are no competing interests.

Figures

Figure 1
Figure 1. Distribution of Elatine populations studied.
For acronyms, see Table 1.
Figure 2
Figure 2. The method of measuring of seed.
(A) surface; (B) profile; (C) rectangle a; (D) rectangle b; (E) the angle of curvature (γ = α + β); (F) number of pits in the middle row.
Figure 3
Figure 3. Boxplots of the most discriminative seed traits among 28 studied populations of Elatine.
Notations: boxes indicate 25–75 percentiles, white point indicate medians, whiskers exclude outliers, black points indicate outliers. For acronyms, see Table 1. (A) surface; (B) profile; (C) rectangle a; (D) rectangle b; (E) angle; (F) pits.
Figure 4
Figure 4. Multidimensional scaling based on a correlation matrix of Mahalanobis distance for seed traits among 28 populations of Elatine.
For acronyms, see Table 1
Figure 5
Figure 5. Boxplots of the most discriminative seed traits among Elatine species studied.
Notations: boxes indicate 25–75 percentiles, white points indicate medians, whiskers exclude outliers, black points indicate outliers. For acronyms, see Table 1. (A) surface; (B) profile; (C) rectangle a; (D) rectangle b; (E) angle; (F) pits.
Figure 6
Figure 6. Morphological relationships of seeds among surveyed Elatine species displayed by Mahalanobis distance-based UPGMA cluster based on the following features: rectangle a, angle of curvature, and number of pits.
For acronyms, see Table 1.
Figure 7
Figure 7. Categorized scatterplot based on canonical analysis value for seeds of the European species of Elatine.
For acronyms, see Table 1.
Figure 8
Figure 8. The diversity in seed coat micromorphology of Elatine alsinastrum (a–alsHu; b, c–alsPL1), E. brochonii (a, b–broMO; c–broSP), E. campylosperma (a, b–camIT; c–camSP), E. gussonei (a, b–gusMAL; c–gusSP), E. hexandra (a, b–hexPL1; c–hexPL2), E. hungarica (a, b–hunR; c–hunSL).
Scale bar = 10 µm. For acronyms, see Table 1. (A–C) E. alsinastrum; (D–F) E. brochonii; (G–I) E. campylosperma; (J–L) E. gussonei; (M–O) E. hexandra; (P–R) E. hungarica.
Figure 9
Figure 9. The diversity in seed coat micromorphology of Elatine hydropiper (a - hydHu, b, c - hydPL1); E. macropoda (a, b -macIT; c–macSP), E. orthosperma (a, b -ortCZ; c - ortFI1), E. triandra (a–triHU; b, c–triPL1).
Scale bar = 10 µm. For acronyms, see Table 1. (A–B) E. hydropiper; (D–F) E. macropoda; (G–I) E. orthosperma; (J–L) E. triandra.
Figure 10
Figure 10. The diversity of seeds of Elatine campylosperma, E. gussonei, E. hydropiper, E. hungarica, E. macropoda.
Scale bar =200 µm. (A–E) E. campylosperma; (F–J) E. gussonei; (K–O) E. hydropiper; (P–T) E. hungarica; (U–Y) E. macropoda.
Figure 11
Figure 11. The diversity of seeds of Elatine orthosperma, E. alsinastrum, E. brochonii, E. hexandra, E. triandra.
Scale bar =200 µm. (A–E) E. orthosperma; (F–J) E. alsinastrum; (K–O) E. brochonii; (P–T) E. hexandra; (U–Y) E. triandra.

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