Malvaceae

Sphaeralcea ambigua
Sphaeralcea ambigua
Plants of San Diego County ©Michael G. Simpson



Hibiscus coulteri
UofAz #341



Hibiscus coulteri
UofAz


Horsfordia alata UofAz

Malva neglecta UofAz 550

Gossipium hirsutum UofAz 5797

Malvaceae:
Pollen of the Malvaceae is spherical, porate and echinate, with a remarkably thick inner wall (endexine).

The pores can be small (1-3 µm) or large (4-6 µm); and the large pores may or may not have an inner thickening (endopore). The pores are rough, rectangular openings in the outer wall (ektexine), but the pores are very sharp and distinct in the inner layer (endexine). (Compare LM & SEM images of Hibiscus, above.) The pores are evenly-spaced along a single line (arc) encircling the pollen grain. If the length of the encircling line equals that of the spherical grain, the grain is triporate. If it is longer, then the grain is 4-porate, 5-porate etc. For Gossipium (cotton) the line is about twice the length of the circumference, and for Malva (for example) the line is several times the length of the circumference.
    - Thompson's baseball-stitching curve
    - Rucker's Curves


Sidalcea neomexicana UofAz
The spines are about twice as long as the wall is thick, and some are hollow(!)(right). "Small spines" are less than twice the height of the wall (see Sidalcea, right), and "large spines" are bottle-shaped at the base and have a conical base or platform made of long columellae (see Horsfordia, above right). Both lengths of the tapered "spines" have rounded tips.

The columellae are loosely attached to the endexine, and detached endexines and ektexines occur in fossil samples. The surface sculpture is "roughened", but is not distinctive in light micrographs due to the pattern produced by the collumellae.

Some Morphological Groups

  Small Pores Large Pores without endopore Large Pores with endopore
Spines with raised bases   Sida 3 (4) pores
Horsfordia, Malvastrum, Sphaeralcea
4-5 pores
Abutilon, Gayoides, Iliamna, Malacothamnus
8-12 pores
Gossipium
Spines without platforms Lavatera, Malva, Sidalcea Hibiscus, Sida  

Horsfordia alata
UofAz
3 large pores with endopores, large spines.

Sphaeralcea emoryii
UofAz
3 large pores with endopores, large spines.

Sphaeralcea ambigua
UofAz
3 large pores with endopores, large spines.

Malva borealis
UofAz
Small pores and small spines

Gossipium hirsutum
UofAz 375
Large pores with endopore, large spines.

Plants:
The Malvaceae is a cosmopolitan plant family of about 80 genera and nearly 1500 species of herbs, shrubs and trees. The bisexual flowers have 5 petals, an ovary with two carpels, and many stamen. Fruits may be berrys, samaras, schizocarps, or capsules. The leaves are characterized by stellate hairs. Economically important taxa include cotton (Gossipium), okra (Abelmoschus), and many ornamental flowers.

Pollen light micrograph:
The pores and spines are very distinctive allowing the grains to be readily identified to the species or species-group level.

Pollen scanning electron micrograph (SEM)
The characteristic endopores are not visible in SEMs, but the frequent separation of the inner and outer wall allows spectacular photographs of the pollen wall structure.

Production and Dispersal:
This insect pollinated family has low production and poor dispersal, but the plants are so widespread that a few grains appear in many samples.

Preservation:
Good. The walls are very thick, but can break apart.

Fossil Occurrence:
Tertiary (Eocene) onward (Malvacipollis). The Sphaeralcea-type, containing other genera, is

References:
  • Barath, O.M. 1975. Catalogo sistematico dos polens das plantas arboreas do Brasil Meridional XVII - Malvaceae. Memorias do Instituto Oswaldo Cruz 73: 1-29.
  • Culhane, K.J. and Blackmore, S. 1988. Malvaceae: The Northwest European Pollen Flora, 5. Elsevier Science Publishers, Amsterdam, The Netherlands. (Reprinted from Review of Palaeobotany and Palynology 57: 45-74.)
  • Nair, P.K. 1962. Pollen grains of Indian plants - III. (Malvaceae Bombacaceae) Bulletin of the National Botanic Gardens No. 63.
  • Saad, S.I. The sporoderm stratification in the Malvaceae. Pollen et Spores 2: 13-41.

Links
Owen Davis 6/02