Dioon Lindl. Edwards Bot. Reg. 29: misc. 59-60 (1843);
from the Greek dis two and oon eggs, in reference to the paired seeds.
Type: Dioon edule Lindl.
- Platyzamia Zucc., Abh. Math.-Physik. Cl. Konigl. Bayer. Akad.
Wiss. 4: 23, t. 4 (1845). Type: Platyzamia rigida Zucc.
A genus of 11 described species with several unresolved complexes, in the family
Mexico, Honduras & Nicaragua
- Leaves pinnate
- Leaflets lacking a midrib
- Leaflets not articulated
- Sporophylls not in vertical rows in cones
- Megasporophyll apices broadly flattened, upturned, overlapping
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Habit: dioecious palmlike shrubs with aerial or subterranean,
pachycaul, cylindrical stems, with usually many leaves. Leaf bases
persistent or shedding to leave smooth bark in different species. Basal offsets ("suckers")
produced by most species, aerial branching uncommon.
Leaves: pinnate, spirally arranged, interspersed with cataphylls,
lower leaflets often reduced to spines. Petioles lacking prickles, usually swollen at the base.
Longitudinal ptyxis erect,
horizontal ptyxis erect. Leaflets simple, frequently with spiny
margins, with numerous bifurcating parallel
veins and no distinct midrib, leaflets broad-based, not articulated,
inserted near the edges of the rhachis towards the adaxial side,
lacking a differently coloured basal gland; stomata
on lower surface only or on both surfaces; epidermal cells elongated
parallel to long axes of leaflets. Leaves pubescent, at least
when young, with branched or simple transparent hairs.
Microsporophylls: spirally aggregated into determinate, stalked
male cones and each with a simple sterile apex, which is
flattened and upturned. Each microsporophyll bearing
numerous microsporangia (pollensacs) on its abaxial surfaces.
Microsporangia opening by slits. Pollen cymbiform, monosulcate.
Megasporophylls: spirally aggregated into determinate, stalked
female cones. Sporophylls with a simple
dilated apex which is flattened and upturned.
Ovules two (rarely three), stalked, orthotropous, inserted
on the inner (axis-facing) surface of the thickened lamina and
directed inwards ("inverted").
Seeds: subglobular to oblong or ellipsoidal, with a white or cream
fleshy outer sarcotesta. Endosperm
haploid, derived from the female gametophyte. Embryo straight;
with 2 cotyledons that are usually united at the tips and a very
long, spirally twisted suspensor. Seeds radiospermic; germination
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return to the original query, and gradually add more characters.
- 1 Leaflets falcate, especially nearer to the petiole
- 2 Leaflets more than 5 mm wide --
2* Leaflets less than 5 mm wide --
- 1* Leaflets straight
- 3 Leaflets less than 15 mm wide
- 4 Leaflets with entire margins --
4* Leaflets with spinescent margins
- 5 Leaflets at ca 90 deg to rachis
- 6 Leaflets 10-12 mm wide, overlapping --
6* Leaflets 7-9 mm wide, not overlapping --
- 5* Leaflets at 45 deg or less to rachis
- 7 Leaflets less than 5 mm wide, not overlapping; leaves flat --
7* Leaflets more than 5 mm wide, overlapping; leaves keeled
- 8 Leaflets 7-8 mm wide --
8* Leaflets 8-10 mm wide --
- 3* Leaflets more than 15 mm wide
- 9 Petiole spine-free --
9* Petiole spinescent
- 10 Leaflet margins entire --
10* Leaflet margins spinescent --