Weberocereus Britton & Rose

Ruiz-Dominguez, Catalina, Vovides, Andrew P. & Sosa, Victoria, 2019, Systematic relevance of pollen morphology in tribe Hylocereeae (Cactaceae), PhytoKeys 128, pp. 121-140 : 128-131

Weberocereus Britton & Rose

Pollen.

pantocolpate, radially symmetrical, isopolar with convex-cuadrangular contour in polar view. Shape: prolate-spheroidal (P/E=1.07). Apertures: 12-15, brevi colpate, small; polar area large (PAI=0.56). Measurements: pollen grains large, (77.07)82.94(89.61) × (82.67)88.73(98.94) μm in equatorial view; exine thickness (1.96)2.43(2.85) μm. Ornamentation: smooth surface with tectum perforate, ornated with spinules of (1.24)1.41(1.58) μm length × (1.28)1.65(1.91) μm diameter in base; perforations (0.17)0.28(0.45) μm in diameter ( Figure 4B ).

Species examined.

Weberocereus tunilla (F.A.C. Weber) Britton & Rose (Costa Rica, Cartago. C.K. Horich BGA 58344 MEXU).

Qualitatitative pollen characters.

Of the fourteen characters examined, five were identified as variable: Amb (the outline of a pollen grain seen in polar view), colpi number, aperture type (colpate or brevicolpate pollen), marginate exine (an area of the exine around an ectocolpous that is differentiated from the remainder of the exine by difference in thickness and the presence of spinules). The other qualitative characters were not variable (Table 1 , Suppl. material 1: Table S1). Pollen grains of the studied species in tribe Hylocereeae are oblate-spheroidal, tricolpate with spinules of variable size ( Figs 3 and 4 ). Weberocereus , Pseudorhipsalis , and Kimnachia differ from the rest of the tribe by having pollen grains with a small aperture, brevicolpate, with differences in the number of colpi as well. Aporocactus , Acanthocereus , Disocactus , Epiphyllum , and Selenicereus (including Hylocereus ) have tricolpate pollen. In addition, two autoapomorphic characters were identified: convex-quadrangular outline in Weberocereus , marginate exine in Pseudorhipsalis ( Figs 3 , 4 ).

Continuous pollen characters.

The size of pollen grains for the 27 taxa examined varies from 55.47 to 154.42 μm in polar axis, and this is large according to Erdtman (1952). Boxplot diagrams ordered by median values found gaps for spinule length and perforation diameter based on the first and third quartiles ( Fig. 5 ). These were coded based on the simple gap method by Almeida and Bisby (1984). Spinule length differentiates Kimnachia from Pseudorhipsalis . For Selenicereus ( Hylocereus clade), spinule length was found to be polymorphic because it includes representatives lacking spinules and representatives with spinules of larger dimensions than those of Kimnachia and Pseudorhipsalis (Table 1 ).

Multivariate analyses.

The PCA graph displays projections of pollen characters in a multidimensional space in which the first two components explained 62.4% of the observed variance. PC 1 explains 44% of the variance and is associated with size (equatorial diameter, polar axis, and spinule dimensions), while PC 2, which explains 18.4% of the variance, is associated with proportions (PAI and PE ratios) ( Fig. 6A ). The length of the arrows in Figure 6A indicates adequate sampling for all characters, except for exine length (EL) and perforation diameter (PD). The size of pollen grains in the polar and in equatorial views had a positive correlation and, similarly, there is a negative correlation between the PE and PAI ratios, as expected in spherical forms. There is a negative correlation between exine length (EL) and the other measures. Figure 5B displays the species studied along the principal components in relation to pollen characters. The association of species is defined by the size of the pollen grain and its shape from prolate to oblate spheroidal). A core association of species is formed by representative species from all genera, including pollen mainly subprolate to prolate-spheroidal. The only species with no representatives in the core group and that appear as outliers are Pseudorhipsalis amazonica and Kimnachia ramulosa , with prolate to oblate pantocolpate pollen. Remarkably, Selenicereus (Hylocereus) megalanthus , along with S. setaceus are two of the species with prolate-spheroidal pollen grains with the largest polar axis; S. minutiflorus K. ramulosa have the smallest pollen grains (smallest polar axis). Selenicereus minutiflorus is the representative of Selenicereus (Hylocereus) with the unique characters of suboblate pollen and an exine lacking spinules ( Fig. 3 ).

Figures

Figure 3. Pollen grains of tribe Hylocereeae (Scanning Electron Microscope photographs). Left polar view, right equatorial view A Acanthocereus tetragonus (C. Ruiz et al. 576) B Disocactus ackermanii (R. Torres et al. 309) C Epiphyllum oxypetalum (C. Ruiz et al. 640) D Selenicereus costaricensis (C. Ruiz et al. 555) E S. escuintlensis (C. Ruiz et al. 635) F S. guatemalensis (M. Veliz et al. 20227) G S. minutiflorus (C. Ruiz et al. 627) H S. ocamponis (M. Chazaro 7334) I S. polyrhizus (C. Ruiz et al. 566) J S. sp. (C. Ruiz et al. 608).

Figure 4. Pollen grains of tribe Hylocereeae (Scanning Electron Microscope photographs). A-D: Left polar view, right equatorial view A S. undatus (C. Ruiz et al. 560) B Weberocereus tunilla (C. K. Horich BGA 58344) C S. setaceus (H. Bravo et al. 2755). D-J: left polar view, left details of spinules and perforations D S. megalanthus (C. Ruiz et al. 563) E S. stenopterus (C. K. Horich s. n.) F S. triangularis (C. Gomez-Hinostrosa 2110) G Kimnachia ramulosa (L. Velasquez et al. 4884) H Pseudorhipsalis amazonica (E. Gudino 145) I S. alliodorus (A. Ruiz Velazco et al. 86) J S. glaber (C. K. Horich BGA 57239).

Figure 5. Box plots of two coded pollen characters, which are discriminant for genus in tribe Hylocereeae. A Spinule length B perforation diameter. Boxes represent the first and third percentiles and black lines indicate median values. Character states are indicated (0, 1 and 2) for each character and measurement range is indicated. Measurements are in µm.

Figure 6. Principal Component Analysis graph. A Scatterplot displaying projections in a multidimensional space of the pollen grain characters: Apocolpium (A), Mesocolpium (M), Equatorial diameter in polar view (EDP) Exine length (EL), Polar Area Index (PAI), Equatorial diameter (ED), Polar axis (PA), Shape class (PE), Spinule length (SL), Spinule base (SB), Perforation diameter (PD). PC 1 explains 44 % of the variance and PC 2 explains 18.4 % of the variance B Sorting of the 27 species of tribe Hylocereeae, in relation to the morphometric variables of pollen grains.