Penstemon 13 Copenhagen Bot Garden 130821 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon 1b Rancho Santa Ana Botanic Garden, Los Angeles 130406 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon 2b Rancho Santa Ana Botanic Garden, Los Angeles 130406 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon 3 Rancho Santa Ana Botanic Garden, CA 130406 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon 4a Rancho Santa Ana Botanic Garden, CA 130406 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon 4b Rancho Santa Ana Botanic Garden, CA 130406 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon 4c Rancho Santa Ana Botanic Garden, CA 130406 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon 5b Santa Barbara Botanic Garden, CA 130411 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon 5c Santa Barbara Botanic Garden, CA 130411 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon 7 Copenhagen Bot Garden 120919 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon 8c Santa Barbara Botanic Garden, CA 130411 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon 8d Santa Barbara Botanic Garden, CA 130411 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon 8e Santa Barbara Botanic Garden, CA 130411 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon 9b Santa Barbara Botanic Garden, CA 130411 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon 9c Santa Barbara Botanic Garden, CA 130411 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon 9d Santa Barbara Botanic Garden, CA 130411 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon barbatus 6 Lund Bot Garden 120704 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon campanulatus 1 Copenhagen Bot Garden 130625 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon campanulatus 5 Copenhagen Bot Garden 130611 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon campanulatus 6 Copenhagen Bot Garden 130611 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon cardwellii 1 Copenhagen Bot Garden 130611 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon cardwellii 2 Copenhagen Bot Garden 130611 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon cf centranthifolius 3 Anza, CA 130417 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon cf centranthifolius 4 Anza, CA 130417 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon cf fruticosus ssp scouleri 3 Copenhagen Bot Garden 130516 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon cf utahensis 2 Lund Bot Garden 150713 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon cobaea 2 Copenhagen Bot Garden 080710 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon confertus 1 Copenhagen Bot Garden 130611 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon davidsonii 1 Lund Bot Garden 160721 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon davidsonii 2 Lund Bot Garden 160721 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon davidsonii 3 Lund Bot Garden 160721 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon davidsonii 4 Lund Bot Garden 160721 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon davidsonii 5 Lund Bot Garden 160721 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon davidsonii 6 Lund Bot Garden 160721 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon digitalis 11 Lund Bot Garden 150731 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon digitalis 4 Copenhagen Bot Garden 130625 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon digitalis 5 Copenhagen Bot Garden 120926 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon digitalis 6 Copenhagen Bot Garden 120926 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon digitalis 9 Lund Bot Garden 150731 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon eriantherus 1 Copenhagen Bot Garden 080710 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon eriantherus 2 Copenhagen Bot Garden 080710 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon euglaucus 4 Copenhagen Bot Garden 120926 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon fruticosus 1 Copenhagen Bot Garden 130604 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon fruticosus 2 Copenhagen Bot Garden 130604 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon fruticosus var scouleri 2 Lund Bot Garden 130619 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon hartwegii Bergianska, Stockholm 060821 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon heterophyllus 1 Copenhagen Bot Garden 130611 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon heterophyllus 2 Copenhagen Bot Garden 130611 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon heterophyllus 4 Copenhagen Bot Garden 080710 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon heterophyllus 5 Copenhagen Bot Garden 080710 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon hirsutus 1 Copenhagen Bot Garden 080710 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon hirsutus 4 Copenhagen Bot Garden 130625 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon hirsutus 5 Copenhagen Bot Garden 130625 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon hirsutus 6 Copenhagen Bot Garden 080710 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon hirsutus 7 Copenhagen Bot Garden 080710 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon hirsutus 8 Copenhagen Bot Garden 120926 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon kunthii 3 Lund Bot Garden 150713 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon ovatus 3 Copenhagen Bot Garden 120926 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon panoche 1 Santa Barbara Botanic Garden, CA 130411 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon panoche 2 Santa Barbara Botanic Garden, CA 130411 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon panoche 3 Santa Barbara Botanic Garden, CA 130411 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon parryi 1 Desert Botanical Garden, Phoenix, Arizona 130426 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon parryi 2 Desert Botanical Garden, Phoenix, Arizona 130426 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon pinifolius 3 Copenhagen Bot Garden 130611 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon procerus Copenhagen Bot Garden 080710 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon serrulatus 10 Copenhagen Bot Garden 150626 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon serrulatus 11 Copenhagen Bot Garden 150626 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon serrulatus 3 Copenhagen Bot Garden 080710 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon serrulatus 4 Copenhagen Bot Garden 130625 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon serrulatus 5 Copenhagen Bot Garden 130625 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon serrulatus 6 Copenhagen Bot Garden 130625 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon serrulatus 8 Copenhagen Bot Garden 150626 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon serrulatus 9 Copenhagen Bot Garden 150626 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon whippleanus 1 Copenhagen Bot Garden 140625 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon whippleanus 2 Copenhagen Bot Garden 140625 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon whippleanus 3 Copenhagen Bot Garden 140625 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon whippleanus 4 Copenhagen Bot Garden 140625 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

cf Penstemon 1a (cult), Zoological Garden, Phoenix, Arizona 130427 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

cf Penstemon 1b (cult), Zoological Garden, Phoenix, Arizona 130427 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

cf Penstemon 1c (cult), Zoological Garden, Phoenix, Arizona 130427 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

cf Penstemon 1d (cult), Zoological Garden, Phoenix, Arizona 130427 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

cf Penstemon 1e (cult), Zoological Garden, Phoenix, Arizona 130427 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon 10a Santa Barbara Botanic Garden, CA 130411 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon 10b Santa Barbara Botanic Garden, CA 130411 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon 11 Desert Botanical Garden, Phoenix, Arizona 130426 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon 14 Copenhagen Bot Garden 130625 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon 1a Rancho Santa Ana Botanic Garden, Los Angeles 130406 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon 2a Rancho Santa Ana Botanic Garden, Los Angeles 130406 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon 5a Santa Barbara Botanic Garden, CA 130411 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon 6a Desert Botanical Garden, Phoenix, Arizona 130426 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon 6b Desert Botanical Garden, Phoenix, Arizona 130426 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon 6c Desert Botanical Garden, Phoenix, Arizona 130426 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon 8a Santa Barbara Botanic Garden, CA 130411 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon 8b Santa Barbara Botanic Garden, CA 130411 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon 9a Santa Barbara Botanic Garden, CA 130411 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon alpinus 1 Copenhagen Bot Garden 130611 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon alpinus 2 Copenhagen Bot Garden 130611 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon alpinus 3 Copenhagen Bot Garden 130611 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon azureus 1 Lund Bot Garden 160520 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon azureus 1 Lund Bot Garden 160530 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon azureus 2 Lund Bot Garden 160520 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon azureus 2 Lund Bot Garden 160530 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon barbatus 1 Copenhagen Bot Garden 080710 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon barbatus 2 Copenhagen Bot Garden 080710 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon barbatus 3 Bergianska 060821 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon barbatus 4 Lund Bot Garden 120704 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon barbatus 5 Lund Bot Garden 120704 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon campanulatus 2 Copenhagen Bot Garden 130611 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon campanulatus 3 Copenhagen Bot Garden 130611 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon campanulatus 4 Copenhagen Bot Garden 080710 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon cf centranthifolius 1 Anza, CA 130417 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon cf centranthifolius 2 Anza, CA 130417 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon cf centranthifolius 5 NW Ocotillo, CA 130422 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon cf centranthifolius 6 NW Ocotillo, CA 130422 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon cf fruticosus ssp scouleri 1 Copenhagen Bot Garden 130516 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon cf fruticosus ssp scouleri 2 Copenhagen Bot Garden 130516 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon cf utahensis 1 Lund Bot Garden 150713 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon cobaea 1 Copenhagen Bot Garden 080710 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon confertus 2 Copenhagen Bot Garden 130611 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon confertus 3 Copenhagen Bot Garden 130611 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon digitalis 1 Copenhagen Bot Garden 130625 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon digitalis 10 Lund Bot Garden 150731 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon digitalis 12 Lund Bot Garden 150731 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon digitalis 2 Copenhagen Bot Garden 120926 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon digitalis 3 Copenhagen Bot Garden 080710 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon digitalis 7 Lund Bot Garden 150731 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon digitalis 8 Lund Bot Garden 150731 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon eatonii 1 Desert Botanical Garden, Phoenix, Arizona 130426 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon eatonii 2 Desert Botanical Garden, Phoenix, Arizona 130426 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon eatonii 3 Desert Botanical Garden, Phoenix, Arizona 130426 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon euglaucus 1 Copenhagen Bot Garden 130604 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon euglaucus 2 Copenhagen Bot Garden 080710 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon euglaucus 3 Copenhagen Bot Garden 130604 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon euglaucus 5 Copenhagen Bot Garden 130604 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon fruticosus var scouleri 1 Lund Bot Garden 130619 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon glaber 1 Lund Bot Garden 080618 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon glaber 2 Lund Bot Garden 080618 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon gracilis Bergianska, Stockholm 051006 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon heterophyllus 3 Copenhagen Bot Garden 080710 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon heterophyllus 6 Copenhagen Bot Garden 150626 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon heterophyllus 7 Copenhagen Bot Garden 150626 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon heterophyllus 8 Copenhagen Bot Garden 150626 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon hirsutus 2 Copenhagen Bot Garden 130611 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon hirsutus 3 Copenhagen Bot Garden 130625 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon kunthii 1 Lund Bot Garden 150713 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon kunthii 2 Lund Bot Garden 150713 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon ovatus 1 Copenhagen Bot Garden 130625 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon ovatus 2 Copenhagen Bot Garden 130625 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon pinifolius 1 Copenhagen Bot Garden 130611 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon pinifolius 2 Copenhagen Bot Garden 130611 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon serrulatus 1 Copenhagen Bot Garden 130625 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon serrulatus 2 Copenhagen Bot Garden 130625 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon serrulatus 7 Copenhagen Bot Garden 150626 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon strictus 1 Bergianska, Stockholm 060821 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Penstemon strictus 2 Bergianska, Stockholm 060821 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).