Page 6 - Bulletin of the Cupressuss Conservation Project vol04_nr1 2015

Typical pollen cones of Podocarpus gnidioides are unbranched structures limited in growth and
carrying several hyposporangiate sporangiophores, which are inserted directly at the cone-axis as is
also the case in all other Podocarpus species (e.g. KRÜSSMANN 1983, DALLIMORE & JACKSON
1966, MUNDRY 2000, MUNDRY & MUNDRY 2001, FARJON 2010, DÖRKEN et al. 2011) and in nearly
all other coniferous taxa. Most authors regard the coniferous microsporangiophores as
microsporophylls and thus, unbranched pollen cones fulfill the definition of “flowers”. However,
also some of the investigated pollen cones of Podocarpus gnidioides had a branched structure
developing 1 or 2 lateral units in the basal part, each of them developed from different buds, so that
the base of each lateral cone-axis is also surrounded by bud scales. This is a great difference to
other coniferous taxa showing branched pollen cones e.g. Cephalotaxus (Taxaceae). In
Cephalotaxus the whole “inflorescence” is developed from a single bud. Thus, bud scales are only
developed at the base of the stalk of the complete cone.

The microsporangiophores of Podocarpus gnidioides differ from other coniferous
microsporangiophores by lacking intercellular spaces, which are distinctly developed for example
in microsporangiophores of Pinus (MUNDRY 2000). The change in the orientation of maturing
microsporangia and their final position is quite different among recent conifers, sometimes even
within a genus. MUNDRY (2000) has shown that in Podocarpus macrophyllus the young developing
microsporangia are first orientated parallel to the stalk, perhaps due to a lack of space within the
young, developing cone. In late ontogenetic states, when the cone-axis elongates, the sporangia turn
in a more or less vertical position to the stalk. The orientation of ripe microsporangia of Podocarpus
gnidioides differs strongly from Podocarpus macrophyllus. In Podocarpus gnidioides even the ripe
sporangia are orientated parallel to the central stalk of the microsporangiophore. In this respect
Podocarpus gnidioides is quite similar to Pinus. In Pinus young sporangia are developed parallel to
the central stalk and keep this position also at maturity. It seems that in Podocarpus gnidioides this
position is caused due to the lack of space even within ripe cones. For a successful release of the
airborne pollen a vertical position of sporangia as developed in Podocarpus macrophyllus is more
favourable. The microsporangia open along a preformed longitudinal line which is also more or less
vertical to the central stalk and thus well exposed to the airflow. Thus a huge amount of pollen can
be released by the microsporangia. In this respect the parallel orientation of microsporangia as
developed in Podocarpus gnidioides (fig. 3A) or Pinus is not so favourable. The sporangia also
open along a longitudinal preformed line, which is developed, however, parallel to the central stalk
of the sporangiophore (fig. 3A) and therefore in some parts deeply placed within the cone. Thus,
only a small amount of pollen can be released from the sporangia by the wind. In taxa with parallel
orientated microsporangiophores the pollen is presented secondary. The released pollen is first
collected especially on the adaxial side of the scutellum of the lower microsporangiophores. From
here the pollen is taken by the wind.

The number of microsporangiophores in pollen cones of Podocarpus gnidioides (83-126) is slightly
lower compared to closely related taxa. In this respect, pollen cones, e.g. of Podocarpus totara with
100-120 microsporangiophores, are quite similar to Podocarpus gnidioides (WILSON & OWENS
1999). In other Podocarpus species with large pollen cones the number of inserted
microsporangiophores can reach up to 284 (SCHULZ et al. 2014). Thus, with only 83-126
microsporangiophores per pollen cone Podocarpus gnidioides has one of the smallest pollen cones
among recent Podocarpus species.

Each microsporangium produces several bisaccate pollen grains as in all other Podocarpus-species
(e.g. SPORNE 1965; TOMLINSON et al. 1991; OWENS et al 1998; GELBART & VON ADERKAS 2002;
FERNANDO et al. 2010; LESLIE 2010). The bisaccate pollen grains correlate well with the downward
facing micropyles and secretion of a pollination drops. The sacci help the pollen grains floating
upward in the pollination drops. Thus the pollination mechanism in Podocarpus is similar to several
Pinaceae, e.g. Cedrus, Pinus or Picea, albeit with a different seed cone morphology (e.g. SPORNE
1965; TOMLINSON et al. 1991; OWENS et al. 1998; GELBART & VON ADERKAS 2002; FERNANDO
2010; LESLIE 2010).

Bulletin CCP, vol. 4, n° 1. ─ 39 ─