what plants are originated in Alaska?

Question

And why

Answer 1

I am not positive whether you are asking for a list of native plant species (endemics), or whether you are asking a question about plant evolution. If you are just wanting a list of native species, search google on natives and/or endemic plants of Alaska.

An Alaskan botanist could answer this question much better, but here goes:
It is much easier to say whether a plant is native or endemic to Alaska (ie-there before ~17th century), than to determine where it originated (evolved, first appeared in the earth's record). Knowing where a plant originated (evolved) is difficult because many ranges of plants were once different than they are now. So, a species now found only at locality A, could have once have a much wider distribution and occurred at localities B and C as well. On the other hand, large areas of Alaska were covered by glaciers and snow during the Pleistocene (last Ice Ages). So, plants migrated in as the ice receded.

The plant Primula egaliksensis species complex is endemic and is only found in Alaska. Here's a websites that includes some discussion of research to determining origin and history of the species development from Pleistocene time.
http://www.systbot.unizh.ch/institut/personen/person.php?id=24&s=alpine

Here is some information about unique plant communities: from the National Park Service website for Wrangell-St. Elias.
“The south-facing bluffs along the White, Nabesna, Chitina and Copper Rivers are similar to the steppe found in Yukon-Rivers National Preserve, but not as extensive. Numerous rare and endemic plant species have been found in these communities, which may be refugia. Other plant communities in the park associated with unique landforms and lithologies such as sand dunes, mud volcanoes, volcanic ash, limestone, lakes and wetlands harbor uncommon species and species with disjunct distributions. Alaska-Yukon endemic species are more common in the Alaska Range and northern Wrangell Mountains. This trend corresponds to our understanding of plant migration after the Pleistocene Epoch from refugia in the upper Yukon Valley, the Alaska Range and Beringia, the northern part of the Park being closest to these migration corridors. In addition, there may have been unglaciated refugial areas within the Late Wisconsin ice sheet adjacent to Lake Ahtna in the northwestern region of the park, and in the dry northern interior of the Park bordering the Tanana Valley and the southeastern edge of Beringia. These refugial communities and communities with rare plants and disjuncts may be at the edges of their ranges and may be more sensitive to environmental changes.”

Here’s something from NPS wesbsite for Denali:
Alaska stands at a floristic crossroads between Asia and North America. During the past two million years, this area has been predominantly associated with the biota of northeastern Asia as opposed to that of North America. This is because the periodic formation of continental ice sheets thousands of feet thick (which covered most of Canada and parts of the northern continental U.S.), has separated Alaska from continental North America on many occasions during this period of time. At the same time, the exposure of the Bering Land Bridge allowed plants and animals a wide dispersal corridor into Alaska from northern Asia. For this reason, many of the plant species of Denali occur in Alaska and northern Asia, but not elsewhere in North America. These plants are known as Beringian endemic species – species that occur only within the large region that was free of ice during the Pleistocene glacial advances.