As a species, juniper could work.
Although the J. scopulorum shown here next to P. ponderosa is not a ground cover type, there are others such as Juniperus horizontalis.
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hey mommy.. daddy here ...

what kind of soil ...

are the trees touching the ground.. or limbed up.. how far up ....

odds are.. if they touch the ground.. there isnt going to be a lot of light in there .... but then you probably wouldnt need a ground cover ...

any chance at a pic ???

any other info would help ...

also .. how big are the pines.. the issue is going to be how much moisture will be available.. under very large mature trees that tend to shed the water to the edges of the canopy ...

are you willing to water heavily .. and mulch properly .. which pine actually do with shed needles.. but a little more will help ...

ken

Yesterday, I saw some cool groupings of Ponderosa with wild lilac (just now forming flower buds) and California coffee-berry at the base.

I imagine that a low-growing Manzanita or Toyon (Christmas Berry) would work very well, too.

Josh

Here are some rules then some recommendations:

Do not plant, irrigate or disturb the soil within 10 feet of the trunk; Plant sparingly; use drip irrigation or soaker hoses, not sprinklers (Sunset Western Garden Book)

I don't know the zones of these - you'll need to look them up).
Arctostaphylos MANZANITA
Berberis darwinii DARWIN BARBERRY
Carpenteria californica BUSH ANEMONE
Ceanothus WILD LILAC
Cistis (Some) ROCKROSE (Cistus crispus) is shown.
Eriogonum WILD BUCKWHEAT
Grevillea rosmarinifolia ROSEMARY GREVILLEA
Holodiscus discolor OCEAN SPRAY
Myrica californica PACIFIC WAX MYRTLE
Myrtus communis TRUE MYRTLE
Nandina domestica HEAVENLY BAMBOO
Cotoneaster
Juniperus JUNIPER
Dryopteris arguta CALIFORNIA WOOD FERN
Hemerocallis DAYLILLY
Heuchera CORAL BELLS
Iris, Pacific Coast and hybrids
Nephrolepis cordifolia SOUTHERN SWORD FERN
Sedum (most) STONECROP
Sisyrinchium bellum BLUE-EYED GRASS
Thymus THYME
Salvia (most) SAGE
Santolina chamaecyparissus LAVENDER COTTON

"Plants for Under Oaks" (same difference, really)
Sunset Western Garden Book (Fifth Printing June 1997); Sunset Books Inc, Menlo Park, CA; ISBN: 0376038519.

Dax

I would think that planting the larger leaved ground covers under the the longer needled Pines would work. That way they would 'eat' the needles. Smaller leaved ground covers for the shorter needled Pines.
Here's what not to do. I planted a Vine Maple under a Ponderosa tree. Look how unsightly the hanging needles are. I'm yanking the Vine Maple and going back to needles as a ground cover. Looks more natural that way.
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