Page 11 - Morphoanatomical investigations of cones and pollen in Cathaya argyrophylla Chung & Kuang (Pinaceae, Coniferales) under systematical and evolutional aspects

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Feddes Repertorium 2014, 125, 25–38 Morpho-anatomical investigations of cones and pollen

Racz 2011; Eckenwalder 2009; Farjon 2010a, b; Mundry 4.1.2 Pollen-cones
2000; Williams 2009). Contrasting to all other Pinaceae
Pollen-cones of Cathaya, Picea, Pinus, Larix and Pseu-
on young seed-scales of Cathaya a distinct bulge is
dotsuga are arranged solitary in the axils of leaves on
developed between the two ovules (Fig. 2D, E). In ripe
one or two years old shoots. In Pinaceae pollen-cones
cones this bulge is no longer visible. This bulge was
are surrounded by bud scales. Pinus differs from all
found in the same position on all seed-scales in all in-
other Pinaceae by a sylleptic sprouting of long-shoot and
vestigated cones. The identity of this bulge could not be
pollen-cones. Male cones are never preceded by folious
solved in this study and remains unclear. Further onto-
leaves on the cone axis. With up to 7 cm length and up
genetic studies are necessary, when more material from
to 150 microsporangiophores the pollen-cones of Ca-
several individuals is available. Thus, it remains open if it
thaya are significantly larger than those in Picea, Larix,
might represent the apex of the seed-scale, which has
Pseudotsuga and most species of Pinus. Only Cedrus
been shifted secondarily in the middle of the cone-
has similar large male cones. The pollen-cone size and
scale´s surface, or if it represents perhaps a rudimentary
the number of microsporangiophores in Cathaya are
sterile ovule.
quite similar to Cedrus. However, these two genera
The ovules of Cathaya, Pinus and Picea are charac-
differ distinctly in the arrangement of pollen-cones.
terized by two equally developed micropylar arms
(Fig. 2D, F). In Larix and Pseudotsuga also two, how- 4.1.3 Pollen
ever, strongly unequally developed micropylar arms are In Cathaya, Pinus and Picea pollen grains are bisaccate.
developed. In Larix and Pseudotsuga several unicellular With an overall length (incl. sacci) of 40–55 μm Cathaya
papillae are developed on both micropylar arms so that pollen are medium sized. Compared to the bisaccate
finally a stigmatic tip for pollen capture is formed (Owens pollen of Pinus (40–80 μm) and Picea (65–130 μm)
et al. 1998), a feature that is always absent in Cathaya, (Eckenwalder 2009) Cathaya pollen is relatively small.
Pinus and Picea. In Larix and Pseudolarix a pollination The unique surface microstructure of Cathaya pollen
drop is absent (e.g. Frankis 1988; Owens et al. 1998). In (sacci and corpi with several spines and perforations;
older literature (e.g. Farjon 1990) a pollination drop is leptoma verrucose) can be easily distinguished from all
also described as absent for Cathaya. In this present other bisaccate Pinaceae and also from all bisaccate
study a pollination drop was also not found in Cathaya. Podocarpaceae pollen, even in fossil records (e.g. Sivak,
As the pollination drop in Pinus is formed only between 1976; Xi & Wang 1989; Ferguson et al. 2007; Grimson &
midnight and early morning (Doyle & O’Leary 1935, Zetter 2011; Bouchal 2013). Thus Cathaya pollen cannot
Doyle 1945; McWilliam 1958; Bagnell 1975; Stützel & be mixed up with the pollen of any other genus. This
Röwekamp 1997, 1999; Tomlinson & Takaso 2002; conforms to the results of earlier studies. In respect to its
Leslie 2010), it is unclear whether Cathaya forms a polli- unique pollen morphology Liu et al. (1997) regards the
nation drop at all or if it has been seeked for at the position of Cathaya as isolated among Pinaceae and
wrong time. Orientation of the micropyle as well as the conclusions about the relationships of Cathaya to the
saccate pollen suggest the existence of a pollination other Pinaceae genera based on pollen morphology as
drop in Cathaya as well. A similar pollination process difficult.
occurs in several Podocarpaceae with saccate pollen
(e.g. Salter et al. 2002; Tomlinson 1994; Tomlinson et al. 4.2 Evolutionary implications
1997; Tomlinson & Takaso 2002; Schwendemann et al.
2007; Leslie 2010). In Abies the ovules develop also two Pinaceae pollen-cones are unbranched structures con-
downward orientated micropylar arms similar to those sisting of several spirally inserted hyposporangiate mi-
developed in Cathaya, Pinus and Picea, however a crosporangiophors, with a central stalk, typically two
pollination drop, in which the bisaccate pollen might drift abaxial microsporangia and a phylloid rest. Thus, the
upwards has not been recorded (Owens et al. 1998; pollen-cones fulfill the definition given to a single “flower”
Williams 2009). Seed-cones of most Pinaceae mature in in angiosperms.
the year of pollination as is also the case in Picea, Larix Generally, the evolutionary pathway of coniferous
and Pseudotsuga. Depending from the species in Pinus pollen-cones and their microsporangiophores as well is
the seed-cones mature in the second or third year (Far- still controversially discussed. Some authors regard all
jon 1984, 2010b), those of Cathaya in the second year, coniferous microsporangiophores as homologous struc-
between 16–18 month after pollination, as it has also tures. In this concept the hyposporangiate (dorsiventral)
been reported by Callaghan (2011) and WANG et al. microsporangiophores present derived structures from a
(2012). However, this conflicts with the data given by perisporangiate ancestral condition (e.g. Wordsell 1901;
Farjon (1990), Debreczy & Racz (2011) or Eckenwalder Dupler 1919; Dluhosch 1937). Other authors (Thom-
(2009) who described cones as maturing in a single son 1940; Wilde 1975; Mundry & Mundry, 2001; Dörken
season. et al. 2011) regard perisporangiate microsporangiopho-

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